E.g. [link|http://www.laurelfootandanklecenter.com/sub.php?page=prob_heel_plantar|Laurel Foot and Ankle Center]:
Plantar fasciitis is caused by inflammation of the connective tissue that stretches from the base of the toes, across the arch of the foot, to the point at which it inserts into the heel bone. Also called "heel spur syndrome," the condition can usually be successfully treated with conservative measures such as use of anti-inflammatory medications and ice packs, stretching exercises, orthotic devices, and physical therapy.
Cheers,
Scott.
(Whose wife - who has run for about 30 years - has it pretty bad, and who seems to have a mild case himself.)