Explain what a constant is?

A constant is a fixed value. Because in algebra, a constant is a number on it's own, or sometimes a letter such as a, b or c to stand to stand for a fixed number.

For example: in "x + 5 = 9" are constants.

Another example is: "4x - 7 = 5" The 4 is the coefficient, the x is the variable, the minus sign is the operator, and the 7 and 5 are the constants.  

But if it's not a constant, then it's a variable.

Hope I helped!

- Amber