Unless you've been living under a rock for the past year or so, you've seen the term "Wi-Fi." You've probably figured out that it's shorthand for "wireless fidelity." You may even know that it's got something to do with accessing the Internet or a private network through the air instead of through cables.

What you're probably still wondering is: Why should I care?

Because chances are that, within the next year or so, you'll use Wi-Fi regularly at work, at home, or on the road. You may well depend on Wi-Fi as much as you do your cell phone, your laptop computer, or your personal digital assistant (PDA).

In fact, all those devices increasingly come ready to work with Wi-Fi. (One example: By 2007, according to IDC Research of Framingham, Mass., 98% of all new notebok PCs will be sold with Wi-Fi capability). That means the next time you invest in hardware, you're likely to invest in the Wi-Fi label as well. So it makes sense to learn what Wi-Fi does well -- and where it still needs work.

Wi-Fi refers to products certified to work with the high-tech industry's global standard for high-speed wireless networking (see "Wi-Fi Phrasebook."). Hardware carrying the Wi-Fi logo has passed rigorous testing by the Wi-Fi Alliance, a trade association based in Mountain View, Calif. (see "Resources"). Certification means that, regardless of which company manufactured it, the equipment should play nicely with other Wi-Fi devices and networks.

As Wi-Fi compatibility grows -- to date, the alliance has certified nearly 865 products -- so has its popularity. Currently, about 4.7 million Americans regularly use Wi-Fi, according to Stamford, Conn.-based research group Gartner Inc. In four years, that figure will grow to 31 million users in the United States alone.

Why is Wi-Fi so widespread -- and what's in it for businesses?

It's fast. Wi-Fi's latest version is many times faster than DSL or cable connections, and literally hundreds of times faster than those old dial-up connections. That's particularly handy when you're working on the run, on the road, or from home: If you've ever watched seconds tick by while watching Web pages load, you'll appreciate the potential productivity gain.

It's convenient. As soon as a Wi-Fi-equipped device is within range of a base station, it's online. With no wires, you can move your laptop computer from place to place -- for instance, from your office to a conference room down the hall -- without losing your network connection. (For an online calculator that can help determine ROI on an in-house wireless network," Resources."). When traveling, you can set up shop anyplace equipped with a Wi-Fi network: another company's office, a hotel room, or a convention center.

It's everywhere. Public Wi-Fi access sites -- or "hot spots" -- are multiplying faster than rabbits on Viagra. They're in bookstores, airport lounges, fast-food restaurants (including some McDonald's and Schlotzky's Deli outlets), and coffee shops (including many Starbucks outlets). In addition, local merchants from Cincinnati to Athens, Ga., to Portland, Ore., are footing the bill for bigger hot spots, accessible throughout a business district or neighborhood.

Some companies charge for hot-spot use; others offer free access. All hope they're creating environments where tech-savvy customers will linger -- and, presumably -- spend more money on coffee, books, sandwiches, or whatever the hot-spot host sells. Does the idea pay off? Overall, it's too early to tell. Ultimately, the answer will affect how fast the public hot-spot market heats up. In June 2003, IDC, the Framingham, Mass.-based research company, estimated that the number of commercial Wi-Fi sites would grow 57% annually over the next five years -- but warned that the market is young, volatile, and based on unproven business models. In other words, if hot spots don't generate revenue, expect that growth rate to stall.

For all its wonders, the Wi-Fi world comes with some drawbacks. Among them:

Range: Although you lose the wires, you're still limited to the base station's range, typically 75 to 150 feet indoors and a few hundred feet outdoors, depending on equipment, radio frequency, and obstructions.

Power drain: Networks using early versions of Wi-Fi technology tend to quickly gobble power -- a disadvantage for battery-dependent laptop users.

Interference: Nearby microwave ovens and cordless phones, particularly older models, can slow down Wi-Fi transmissions.

Security: Here's the downside of providing fast, easy access: outsiders can sometimes get into your wireless networks as fast and easily as you can. Check with hardware vendors about the latest security precautions and products. The Wi-Fi Alliance currently recommends using Wi-Fi Protected Access (WPA) technology, which both authenticates users and encrypts data. Look for even tougher security measures within the next year.

Entering the world of wireless fidelity, or Wi-Fi, requires knowing just a little local lingo. Here are the most important terms:

802.11: We're covering this term only because you'll run across it in learning about Wi-Fi. Pronounced "eight-oh-two-dot-eleven," it's usually followed by a letter (mostly a, b, g). Essentially, this is Wi-Fi's technical name. It refers to a family of specifications for wireless LANs. Higher letters indicate more recent, and presumably improved, versions of the technology.

Base station: The heart of a Wi-Fi network, it's equipped with an antenna that sends a low-powered, short-range radio signal. Wi-Fi-enabled devices within a certain radius detect the signal, letting users access the network.

Bluetooth: A specification for very short-range wireless transmission (within 30 feet).

Hot spot: Wi-Fi access point. The term usually refers to coffee shops, airports, hotels, and other public locations with local area networks (LANs) that Wi-Fi-equipped users can access free or for a fee. (To find a hot spot, see "Resources."

LAN: Local area network. A WLAN is a wireless local area network.

Wi-Fi Protected Access (WPA): Wireless network security technology; replaced an older, more vulnerable mechanism known as Wireless Equivalent Privacy (WEP).

As you might expect, the Web is awash in resources about Wi-Fi. Here's a sampling:

Wi-Fi Alliance Main site for the nonprofit trade association behind Wi-Fi certification. Offers a plain-English introduction to Wi-Fi, lists of Wi-Fi certified products, security information, and other resources, including:

Wi-Fi Alliance Benefits Calculator Downloadable spreadsheet helps companies calculate the ROI on their Wi-Fi investments.

Wi-Fi Glossary: One-stop dictionary defines all those strange wireless-networking acronym.