A heel spur is a small osteophyte (bone spur) located on the calcaneus (heel bone). Calcaneal spurs are typically detected by a radiological examination.
When a foot bone is exposed to constant stress, calcium deposits build up on the bottom of the heel bone. Generally, this has no effect on a person’s daily life. However, repeated damage can cause these deposits to pile up on each other,causing a spur-shaped deformity, called a calcaneal (or heel) spur. Obese people, flatfooted people, and women who constantly wear high-heeled shoes are most susceptible to heel spurs.
An inferior calcaneal spur is located on the inferior aspect of the calcaneus and is typically a response to plantar fasciitis over a period, but may also be associated with ankylosing spondylitis (typically in children). A posterior calcaneal spur develops on the back of the heel at the insertion of the Achilles tendon.
An inferior calcaneal spur consists of a calcification of the calcaneus, which lies superior to the plantar fascia at the insertion of the plantar fascia. A posterior calcaneal spur is often large and palpable through the skin and may need to be removed as part of the treatment of insertional Achilles tendonitis. These are also generally visible to the naked eye. Source: Wikipedia