First, you mean "potential" infinity as an adjective, not "potentially", an adverb. You could say "potentially infinite" since "infinite" is an adjective where "infinity" is a noun. (That's your English lesson for today.)
"Actual infinity", often called "completed infinity", applies only to sets: A set is "infinite" if and only if there is no upper bound on the number of objects it contains. "potential infinity" applies to sequences: the sequence 1, 2, 3, … increases without bound so is a "potential" infinity. (Since the two situations are completely different, there is seldom reason to make the distinction!)