Answer:

A Constant is a fixed number, rather than a variable number.

In the equation v = 10t + 15
The numbers 10 and 15 are constants. v and t can be given various values – they are variables.

Mathematical constants are always definable numbers and are almost always also computable numbers (Chaitin's constant being a significant exception). However, computable constants need not be easily computed; the De Bruijn-Newman constant, for example, has no known digits of its decimal expansion.