Definition of field goal:
(n) :
(basketball) A shot that is scored while the ball is in play (i.e. not a free throw).
(n) :
(American football, Canadian football) A kick of the ball through the uprights and over the crossbar (not after a touchdown). It scores 3 points.
(n) :
(rugby) A goal scored where a ball that is in play but on the ground is kicked through the uprights and over the crossbar.