1) one of the upright posts supporting a handrail (baluster)

2) posts with a piece across the top on the outer edge of a staircase (banister)

3) a bar going across, e.g. joining the two posts of a goal in football etc or the front and back parts of a bicycle (crossbar)

4) (in games such as football) the posts between which (the goal-mouth) the ball is to be sent in order to score; an aim of one's effort or ambition (goal)