What exactly is a bone spur?

A bone prominence: Bone spurs can occur anywhere and when not associated with arthritis are usually painless. Sometimes they can cause irritation of a tendon or ligame leading to pain.

Bone build-up: It's a ridge of bone that develops where a tendon or a ligament attaches to a bone after repeated stress. For instance, it can develop in the front of the heel bone in people who are runners, have flat feet and plantar fasciitis. It is called a spur because, when you see it from the side on an x-ray, it looks like a spur rather than a ridge.