constant – a value, number or symbol that remains fixed

To remember the meaning of constant, use the following mnemonic:

It was constantly (constant) raining. We had fixed weather that never changed.

Unlike variables, which can take on different values, a constant always represents the same number throughout a problem or equation. Constants can be specific numbers like 5, -3, or 0.75, or they can be well known mathematical constants with special properties such as π (pi, approximately 3.14159), which represents the ratio of a circles circumference to its diameter, or e (Euler's number, approximately 2.71828), which is fundamental to exponential growth and calculus. 

For example, in an algebraic expression such as 3x + 7, the number 7 is a constant because it remains the same regardless of what value x takes.