"Like terms are terms whose variables (and their exponents such as the 2 in x^2) are the same. In other words, terms that are "like" each other. Reminder: the coefficients of each term can be different. "
5 has x^o and -5 has x^0 LIKE TERMS (x^0 = 1)
-5 has x^0 and -12x has x^1 UNLIKE TERMS
5x has x^1 and -12x has x^1 LIKE TERMS
5x has x^1 and 5y has y^1 UNLIKE TERMS (variables have to have same "letter" and exponent in order to be LIKE TERMS)