A series of American Idiom derived from baseball.
Used primarily by teen and pre-teen boys to indicate what they have done
with their female date. The following is the standard list although there
are variations.
first base: kissing
second base: touching the girl's breasts (some would define this as
kissing with tongues instead)
third base: touching the girl's genitals or putting hand under panties
(some in this hedonistic age would define this as oral sex)
home run / fourth base: having sex.