For many newer no-limit hold'em players, "three-betting" or reraising before the flop is a rarely chosen action, almost exclusively performed (if at all) with the strongest starting hands. For the same group, "four-betting" preflop — that is raising after someone has reraised — is even less commonly done, perhaps only with pocket aces or pocket kings (if the chips haven't gotten in the middle already).
That means when we begin talking about three-betting or four-betting "light" — that is, with medium-strength or even weak starting hands — we've moved into more of an advanced topic to consider.