What does “get to second base with someone” mean?

Rebecca

"Second base" means the physical stages in a romantic/sexual relationship. Usually, "second base" means intimately fondling, touching, and feeling the other person above the waist. There is "first base," "second base," "third base," and "home run." These all represent different stages of a sexual relationship. Ex: They got to second base last night. Ex: He's never even been to second base.