A pockmark is a small, concave scar on a person's skin. Pockmarks can be caused by severe acne.
People who have a lot of pimples as teenagers sometimes end up with pockmarks on their faces as adults. Any serious skin condition — including chickenpox or insect bites — can result in a pockmark. You can also use this word as a verb, either to mean "mark with scars," or to describe something that reminds you of pockmarked skin: "The rain pockmarks the smooth sand on the beach."