Definition of first bases:
(n) :
(baseball) The base after home plate in a counter-clockwise path around a baseball infield.
(n) :
(singular only, US, colloquial) Kissing, regarded as the first phase of a sexual relationship.
(n) :
(singular only, by extension) Completion of the first phase of an activity.
(n) :
(blackjack) The betting spot located immediately to the left of the dealer, which is first to receive cards and first to act.