(from the 8/08 issue of the CompuNerds Nerdsletter - sign up for it here)
GPS stands for Global Positioning System. It uses a system of satellites that send a signal to your receiver which tells you exactly where you are on the planet. The device has maps built in to it and can plot your position on the map. The technology was originally created for the military, but eventually was made available to civilians. It was invented to guide jet fighters and missiles, but now it guides mini-vans as well.
The main use for GPS today are devices that give you driving directions. They use a little screen to show you where you are and what to do next, giving you "turn by turn" directions. They range in price, but they least expensive units currently hover around the $200 price range. The more you spend, the more bells and whistles you get.
They usually have a voice that tells you the directions while you drive. Some have a variety of voices to choose from. Even celebrity voices are available. If you want Dennis Hopper or Mr. T or Gary Busey or John Cleese or Kim Cattrall to direct you to your goal, you're in luck. Some units have real-time traffic data pumped in so that they can route you around accidents or congestion. They'll tell you how far to your destination and when you can expect to arrive. They often have vast libraries of location information stored in them: Points of Interest, or POI's. You could ask your GPS to find you the nearest ATM, or gas station, or post office, Italian restaurant, bowling alley or Starbucks, and it will direct you to it. They even have POI's of speed traps and "safety cameras" so you know where you can expect to receive a speeding ticket. Some will even play music or audiobooks.
The three main brands right now are Garmin, TomTom, and Magellan. The list of possibilities is enormous. As the units get smaller and less expensive, they will show up in more and more devices, such as running shoes, and pet collars. Cell phones too are starting to have GPS built in to them. Some use Google Maps or other software titles to help you find your destination. You can put a tag on your child to see where he or she goes after school, or to keep track of your brood in Disneyland. If you're caravanning on a camp trip, you can keep each vehicle's progress in view. GPS wristwatches are tracking how far and fast you jog, in addition to your pulse and calories burned.
GPS receivers are very easy to use, and they are becoming more prevalent and less expensive all the time. If you don't have one already, you'll probably use GPS in one form or another before too long!