Like terms are terms that have the same variable or terms that can be combined or added together.
2 cars and 3 bikes are not like terms because you cannot combine or add them to get a sum.
You could also say that like terms have exactly the same variable factors or simply the same variables.
For example, 2c and 5c have the same variable factor that is c.
More examples of like terms
5x and 16x
14y and -2y
5 computers and 20 computers
4n and -4n
50 books and 20 books