The term 'variable' has multiple literal and specific meanings, but all are based on common usage. Variable actually means a level of difference between or of a given factor and specific issues or functions relative to that factor. The word can also be used as an infinitive, referring to the state of variance.
Examples of Variable:
'There are too many variables to predict how the market will react.'
The obvious variable in any situation is human behavior.
Statistically, variables are within a 5% range in any market survey.
Product performance contains a natural series of variables in terms of income brackets of the markets to which the product is exposed.