What is the difference between a constant and a coefficient?

Generally, a constant is a standalone number that has no letter, or variable attached to it. A coefficient, on the other hand, is the number the is attached to the variable.

As an example, in ##4x^3+19x^2-5x+21##, 4, 19, and -5 are all coefficients and 21 is the constant. This video also explains this idea:

Let me know if you have any questions, or if anything is unclear. Happy studying!