Explain the term variable

General: a variable is something subject to change or is inconsistant

Science:

a variable is something that depends on another and based on the other thing, changes accordingly.

For example, if you were to do a science experiment: the heat of an object depends on how long it's been sitting there.

in that scenario, the heat is the variable, and the time is an invariable.

an invariable however, is quite the opposite. it is independent of everything and changes on its own terms.