Like Terms

MY definition of a like term is an algebraic expression or term that has the same variables that raised to the same power .one hundred p and three hundred p are like terms because they both have the same variables and for that reason you can combine them . p and p^2 are the same because p^2 is just getting multiplied by it's self and can change like one times so you can not combine it.We can not combine two d and two f because they both have different variables so it can't be alike so we can't combine them . I think a perimeter is a side of a shape added together .A expression is a problem with out a equal sigh .