Some words and letters are such a familiar part of everyday life that they almost fade into the background. From markings on your electronics, food packaging, and clothes to the words you see on water bottles and inside elevators, here are the meanings behind some mysterious letters you might see every day.

Original photo by Mark Collinson/ Alamy Stock Photo

UL

Above-ground red valve unit at defunct nuclear plant with a UL label. — Credit: We Shoot/ Alamy Stock Photo

The letters "UL" can be found on many things, including electric plugs, heaters, smoke alarms, and personal flotation devices. UL stands for “Underwriters Laboratories,” a company that's been conducting product safety testing for more than a century. If an item meets UL's safety standards, it earns the right to bear a "UL" mark.

The man who founded what became UL, William Henry Merrill Jr., got the idea to set up an electrical testing laboratory after being dispatched to check fire risks at the Chicago World's Fair in 1893. The Underwriters Electrical Bureau was founded in 1894, and Underwriters Laboratories was incorporated in 1901. UL began offering its label service to certify products it had tested in 1906.

CE

A CE mark on a computer motherboard. — Credit: Chris Howes/Wild Places Photography/ Alamy Stock Photo

You may have spotted a "CE" on eyeglass frames, mobile phones (or their packaging), appliances, electronics, and more. CE stands for the French phrase "Conformité Européenne," which means “European compliance.” The CE designation indicates an item has met the standards to be sold in the European Economic Area. The certification process ensures that products in specific categories adhere to safety, health, and environmental standards. Placing CE on things isn't required outside of Europe, but plenty of manufacturers leave the CE mark on items that are sold both in Europe and elsewhere.

FCC

Close-up aerial view of an FCC approved product. — Credit: David J. Green/ Alamy Stock Photo

Mobile phones, earbuds, television stations, and other communication devices operate on radio frequencies. In the United States, the Federal Communications Commission checks to make sure these devices can function with no harmful interference. The FCC also ensures a device won't overexpose users to radiofrequency (RF) energy, which is a type of electromagnetic radiation.

After obtaining FCC approval, manufacturers will place an FCC logo on the device and/or its packaging. At first glance, this logo can appear as if it contains just an F and a C next to each other, but a closer look will reveal there's a second C hidden inside the first one.

OTIS

A close-up of the old OTIS elevator control knob. — Credit: Steve Russell/ Toronto Star via Getty Images

Maybe you study the insides of elevators to have something to do during your ascent or descent, or perhaps you get nervous and read every bit of elevator signage in search of reassurance it's working properly. If so, you've likely seen "OTIS" emblazoned on an elevator's floor, control panel, or elsewhere. This isn't an acronym or abbreviation — OTIS refers to the Otis Elevator Company.

In the 1830s and '40s, passengers regularly died in elevators when lifting cables broke. Inventor Elisha Graves Otis created an elevator safety brake, and in 1853, showed off his invention at New York City's Crystal Palace Convention by ascending on an open platform, cutting the hoisting rope with an ax, and not falling thanks to the safety brake. Four years later, E.V. Haughwout and Company's department store in Manhattan became the first business to use elevators equipped with this special brake.

After the Otis Elevator Company was founded in 1853 and Otis patented his invention in 1861, Otis elevators helped transform cities. Today, the company continues to make elevators with the name “Otis” displayed inside. The safety mechanisms in present-day elevators even stick to the same basic engineering principles that Otis originally used.

OU

Close-up of a packet of Heinz ketchup with the OU mark. — Credit: Justin Sullivan/ Getty Images News via Getty Images

People who don't keep kosher may have seen the letter “U” inside a circle on some food items and not have known this indicated the item was processed according to Jewish dietary laws. This letter “U” is actually inside an “O,” not a circle; “OU” stands for “Orthodox Union Kosher.” Some products may be marked with “OU-D” to indicate that they contain dairy or were made on equipment that handled dairy. “OU-P” tells people an item is kosher for Passover.

“OU” isn't the only way to signal that a food item is Kosher. A “K” inside a circle or a star are other well-known marks for kosher foods.

PET

PET mark close up on a bottle, along with an identification symbol for recycling. — Credit: Mameraman/ Shutterstock

You can find the letters "PET" on many plastic bottles, including most of the ones that hold beverages. PET is an acronym for the plastic "polyethylene terephthalate," which is part of the polyester family of polymers.

Above the word "PET" on these bottles, you'll also usually see a 1 in a triangle made up of arrows. This is a recycling code. PET bottles can successfully be recycled, so make sure to do this instead of throwing yours away.

USB

Close-up of a micro SD to SD adapter on a hard disk with a USB drive on top. — Credit: Remus Rigo/ Shutterstock

USB is such a familiar term that you may not be aware it's an acronym for "universal serial bus." USB really did live up to the "universal" part of its name. Before USB, serial ports, parallel ports, and more were used to connect external devices like keyboards, mice, and printers. USB made it possible for these different devices to hook up to computers via the same connection.

USB technology was developed by a group of American businesses, notably Intel, and first became available in 1996. When Apple's iMac came out in 1998, it was a USB-only computer. USB is still popular today, as are USB-C ports on phones, tablets, and certain computers.

YKK

A YKK zipper on a pair black denim jeans. — Credit: Mark Collinson/ Alamy Stock Photo

Zippers are part of our daily lives, whether on our jeans, coats, or bags, and as long as they work, they usually don't receive intense scrutiny. However, a closer look at various zippers will likely reveal that many of them are inscribed with the letters "YKK.”

YKK stands for “Yoshida Kogyo Kabushikikaisha,” which roughly translates to “Yoshida Manufacturing Shareholding Company.” This company, founded in 1934, uses its own brass, polyester, threads, and even zipper machines. By controlling so much of the process, YKK can deliver high-quality zippers. The company also sells these zippers at reasonable prices. The combination has made YKK a go-to in the garment industry — and explains why half of the world’s zippers have YKK zippers.

QR

Couple at a restaurant scanning the menu with QR code. — Credit: Hispanolistic/ iStock

QR codes are those pixelated-looking black-and-white squares that you can scan with your phone for more information about something, whether it’s an advertisement or a piece of art. They’ve become ubiquitous, especially after the COVID-19 pandemic popularized contactless menus and payment. However, they’re very rarely called by their full name.

“QR” actually stands for “quick response,” and the codes can be used to share far more than a link. If you wanted to, you could share an entire book with one code. The technology was first developed by a Toyota subsidiary in the mid-’90s as a way to track auto parts, but QR codes found new life as a way to direct smartphone users from a physical space to a digital one. They used to require a special reader, but nowadays, most smartphone camera apps will read QR codes on their own.

UPC

Closeup of a UPC bar code. — Credit: ImagineerInc/ Shutterstock

You’ve probably noticed a UPC while out shopping, especially if you use self-checkout. It stands for “universal product code.” UPCs have two parts, both of which communicate information to a computer: a barcode, and a 12-digit product code called a Global Trade Item Number, or GTIN.

A product’s GTIN includes a company code for the manufacturer and a product code for the item itself. Manufacturers have to buy each individual code from GS1, a nonprofit industry group that tracks everything. Because all GTIN numbers are 12 digits, companies with a lot of products need shorter company codes to accommodate larger product numbers.

SKU

Warehouse racks with wood stacked to the ceiling. — Credit: jsmith/ iStock

You’ll most commonly see “SKU” in online shopping carts, but occasionally someone will use it as a synonym for “product.” It stands for “stock keeping unit,” and like UPCs, it keeps track of products for sale. Unlike UPCs, which are universal across different companies, a SKU refers to an inventory item internally within one company. Because it’s for internal tracking and not outside purchases, it can be whatever the company wants, but unique SKUs help sellers be more precise about what products they’re stocking, selling, and shipping. In your shopping cart, a SKU identifies the exact color, size, and model of what you’re buying.

PVC

Close-up of PVC tubes. — Credit: sndrk/ iStock

If you’re a crafter or handyperson, you’ve probably come across PVC pipe. Typically, it’s used in water systems from home plumbing to city utilities, but clever DIYers have used it for everything from storage to cosplay, because it’s waterproof, sturdy, durable, and cheap. PVC stands for “polyvinyl chloride.” One of the most-used plastics in the world, it’s also found in insulation, clothing, hoses, toys, and pretty much anywhere that plastic is found.

VR and AR

Woman in virtual reality goggles. — Credit: artiemedvedev/ iStock

You’ve probably seen the terms “VR” and “AR” in arcades, science fiction, and buzzy new technology products. VR stands for “virtual reality,” and refers to an environment that’s entirely simulated. Some gamers use VR headsets to immerse themselves fully in a video game with a full, 360-degree view of a digital world. The tech can also be used to view specially made videos and photography.

AR, or “augmented reality,” adds simulated digital elements to the actual world around you. If you’ve played Pokemon Go — which superimposes Pokemon characters and other game elements on top of your surroundings using a smartphone camera — you’ve experienced an augmented reality application. Live translation apps, which use a smartphone camera to translate text in real time, are another example of AR.

GIF

Download gif button icon isolated. — Credit: VectorV/ iStock

GIF images — that’s Graphics Interchange Format — have been used for more than three decades, although these days they’re mostly used for brief animations. The format was invented in 1987 by the CompuServe internet service provider, and once upon a time it was often used for still images. Because it uses limited colors, it kept file sizes low, which was especially critical when internet speeds were much slower, and it allowed images to have transparent elements, which helped with web design. Most computers and connections can handle bigger file sizes now, and higher-quality formats allow transparency without being prohibitively large — but even today, nothing handles a short clip quite like a GIF.

PU

Leatherette (PU) Multi-color sample. — Credit: peerapong bovornlohachai/ Shutterstock

You may have seen “PU” a lot recently to describe PU leather, a material used to create clothing, accessories, and upholstery. PU stands for polyurethane, a kind of artificial material commonly used in spandex. You also might have seen this acronym in PU foam, which has wide applications from crafting to home repair.

PU leather is a more specific kind of “pleather” or faux leather, which can also be made out of PVC — although PU leather is generally considered to be higher quality and more eco-friendly. It can be vegan, but sometimes includes elements of real leather, too.

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