Definition
From Wikipedia:
A wearable computer is a small portable computer that is designed to be worn on the body during use. In this wearable computers differ from PDAs, which are designed for hand-held use, although the distinction can sometimes be a blurry one. Wearable computers are usually either integrated into the user’s clothing or can be attached to the body through some other means, like a wristband. They may also be integrated into everyday objects that are constantly worn on the body, like a wrist watch or a hands-free cell phone.
Another much quoted definition by Prof. Steve Mann, What is a wearable computer:
A wearable computer is a computer that is subsumed into the personal space of the user, controlled by the user, and has both operational and interactional constancy, i.e. is always on and always accessible. Most notably, it is a device that is always with the user, and into which the user can always enter commands and execute a set of such entered commands, and in which the user can do so while walking around or doing other activities. The most salient aspect of computers, in general, (whether wearable or not) is their reconfigurability and their generality, e.g. that their function can be made to vary widely, depending on the instructions provided for program execution.
With the wearable computer (WearComp), this is no exception, e.g. the wearable computer is more than just a wristwatch or regular eyeglasses: it has the full functionality of a computer system but in addition to being a fully featured computer, it is also inextricably intertwined with the wearer. This is what sets the wearable computer apart from other wearable devices such as wristwatches, regular eyeglasses, wearable radios, etc.. Unlike these other wearable devices that are not programmable (reconfigurable), the wearable computer is as reconfigurable as the familiar desktop or mainframe computer.