"[get|go] to second base with {sb}" の定義と意味

What is the origin of the idiom "get to second base with someone" and when to use it?

The idiom "get to second base with someone" draws its origin from the game of baseball, where the bases represent different stages a player must touch in order to score a run. In a figurative sense, "getting to second base with someone" means engaging in more intimate physical activities of a sexual nature. It suggests a level of physical closeness that goes beyond kissing or basic touching.