In most definitions, a Bluetooth® keyboard is one that uses the Bluetooth® wireless protocol to connect the keyboard to a mobile device, such as a cell phone or a Personal Digital Assistant (PDA). Essentially, any standard QWERTY keyboard that makes use of Bluetooth® could be considered a Bluetooth® keyboard, but the most common definitions limit a Bluetooth® keyboard to one that connects to a small, mobile device that doesn't contain its own keyboard.
The cordless nature of the Bluetooth® keyboard, which typically runs on AA or AAA batteries, makes it quite handy and usable nearly anywhere. In most cases, the Bluetooth® keyboard, which may include a touch pad too, is actually one that can fold up when it isn't in use. This makes it especially easy to carry along with a mobile device.
Keep in mind that most Bluetooth® keyboards are not as large as the standard size you'll see with a computer keyboard or even with a laptop computer. The small size of the keys can make them uncomfortable to use for some people. However, typically they are a better size than those devices that either don't have a keyboard at all, or have one that is so small, use of it is inefficient.
Sometimes, a Bluetooth® keyboard doesn't involve a physical keyboard. For example, I-Tech makes the Virtual Laser Keyboard, which projects a virtual keyboard using laser light onto a table or desk. You then can "type" on the virtual keyboard, and the I-Tech system will record your keystrokes, measuring the location of your fingers as they penetrate the laser light to determine the virtual key you are striking. The I-Tech hardware is small enough to carry, and it connects to your cell phone or PDA through a Bluetooth® wireless connection.
Some desktop computer manufacturers also connect their wireless keyboards to the computer using Bluetooth® technology. This isn't the standard definition of a Bluetooth® keyboard because it's used with a computer, rather than a mobile device. Still, it's technically a keyboard that uses Bluetooth® technology.
Bluetooth® is a wireless communications protocol that allows sending of data over short distances. Bluetooth® can work with multiple devices simultaneously, and connections between devices are simple to make and are usually performed automatically. You'll commonly find Bluetooth® in use with consumer electronics and mobile devices in close proximity. For example, Bluetooth® is commonly used for connecting a wireless headset with your cell phone. It differs from Wi-Fi, which works with wireless broadband Internet connections at home and is designed to work over longer distances.