Spur has two main meanings that both connect to the idea of making something move or happen:

1. A small metal tool with a spiky wheel that horse riders attach to the heel of their boot. When a rider gently presses the spur against the horse's side, it signals the horse to go faster or pay attention. Cowboys in the Old West wore spurs, and you can still hear them jingle in western movies. The phrase to win your spurs comes from medieval times, when a knight had to prove his worth in battle before earning the right to wear spurs.
2. Something that pushes you into action or makes something happen faster. Curiosity might be the spur that makes you research how airplanes fly. A looming deadline can spur you to finish your homework. Scientists sometimes describe one discovery as spurring another, like how the invention of the telescope spurred new understanding of astronomy. When something happens on the spur of the moment, it means you do it suddenly without planning, as if something just spurred you into motion. A spur can also be a ridge that sticks out from a mountain, like the metal tool sticking out from a rider's boot.