Grammatical number

Grammatical number is the way numbers and counting are fitted into sentences.
Most languages have ways to express differences of number. 
Common categories of grammatical number are singular (one) or plural (not one). Some languages, also have a notion of dual, for two, or of paucal, for "a few".
Some languages (like Chinese) do not have the concept of grammatical number, and numbers or other quantifiers are used if necessary. Finally, there may be words that have only one form or are not countable.