The plantar fascia is a thick band of connective tissue that connects the heel bone to the toes. When it gets inflamed, it typically causes heel pain, the classic symptom of plantar fasciitis (PF).
Anybody can get it, but runners are particularly susceptible. The fascia is stretched tight across the bottom of the foot and the repetitive stress of running can cause small tears. Over time, those tears can lead to long-term inflammation and heel pain.