"Like terms" refers to individual terms that have the same variable in them. Also, the variable in
any "like terms" is raised to the same power.
For example: 3x and 10x are like terms (both have the variable x, raised to the 1st power). 14a2 and ba2 are also like terms (both have the variable a, raised to the 2nd power).
This page will show you how to identify and combine like terms.