What does c equal?

In math, a number signified by "C" is a constant number. A constant is the opposite of a variable. While a variable changes, a constant will always stay the same.

For example, in the equation y = 4x + 10, 10 is a constant. If you did not know the value of 10 (for example, if you had just integrated), it could be written as y = 4x + c.