This site is dedicated to handheld computers.
During the 30+ year old history of handheld computers, these devices had different naming: pocket computer, palmtop computer, PDA, electronic organizer, handheld PC, pocket PC, UMPC, MID, smartphone. Each one of these terms emphesizes particular features of the device. For example, the term UMPC means that the device has an x86-compatible CPU. But in general all these terms address the same thing: a small computer, which can be held in hands while operating it. handheld.computer covers all the mentioned kinds of devices.
Someone may also include mechanical computers (like abacus or slide rule), digial media players, programmable calculators or handheld game consoles in the term "handheld computer". Technically that is true. But on this site such devices are out of the scope.