"Well, the Quaffle - that's the biggish red one - is the one that scores goals. Three Chasers on each team throw the Quaffle to each other and try and get it through the goal posts at the end of the pitch - they're three long poles with hoops on the end."
-- Harry Potter explaining Quidditch to Colin Creevey (CS7)
There are three goal posts at each end of a Quidditch pitch – fifty-foot high poles with hoops on them.
The original goal posts were trees, which were then replaced by baskets on poles (QA3).
The role of the Keeper is to keep the other team from scoring goals, but early Keepers could also score by flying to the other side of the pitch (QA6).