Answer
A variable basically works as a "placeholder" for anything that might change a majority of the time.
Examples
In science one may call a factor in a experiment that is subject to change a variable.
In math the term is used for a symbol that we do not know yet, such as x or y. Typically in math a variable is a letter.
In computer programming, variables are used to store information to be referenced and used by a computer program. They do give a way of naming data with a descriptive name as well so programs can be understood more clearly. When you go to assign values to the "variable" you are basically assigning individual variables such as the ones above in a way.