What is a number?
Numbers are mathematical objects that can be counted, measured, and labelled. The most original examples of numbers are the natural numbers, which include 1,2,3,4,5, etc. Aside from counting and measuring, numbers are also used for labels (e.g. telephone numbers), for ordering (serial numbers) and for codes, such as ISBN's. In common usage, a number may also refer to a symbol, a word or an abstract mathematical concept.