A constant is a value that does not change. Typically, a constant will be a real number, but can sometimes be written as a variable. When written as a variable, a constant is commonly denoted as c to represent a fixed value.
y = 2x + 3
In the function above, 3 is a constant. The 2 is a fixed number, but it is more appropriate to call it a coefficient because it is multiplied by x.
y = 5
The term "constant" may also refer to a constant function, or a function whose output value is the same for every input value. The function above is a constant function.
π, e, i, etc.
Some constants are given special symbols because they represent significant values and have important applications across different mathematical fields of study.
Related word constant.