Stricto sensu: inflammation of a bursa. “Bursa” are subcutaneous “bags”, or as “empty pockets” for some joints (the elbow or knee hygroma is also bursitis).
When the skin and the bursa are “trapped” between the bone (exostosis, osteophytes, etc.) and the shoe, this leads to inflammation at their level.
In case of severe conflict, an infection with liquid production can occur: it is called infected bursitis.
