Longman Dictionary of Contemporary English - first base

~ n 1 a) the first of the four places in a game of baseball (1) that a player must touch before gaining a point b) the position of a defending player near this place  (He plays first base for the Red Sox.) 2 AmE informal the first stage of success in an attempt to achieve something  (get to/reach first base)  (You've gotten to first base if you've landed an interview.) 3 get to first base AmE spoken an expression meaning to kiss or hug someone in a sexual way, used especially by young men