A bursa is a pocket of fluid naturally occurring all over the body, offering protection to structures moving over one another. When there is trauma, or increased tissue stress, they can become inflamed. This can result in the area becoming painful, swollen and red, and possibly leaving the area feeling stiff.
As long as the bursa is not infected, NSAIDs, corticosteroids, and/or functional offloading of the area reducing tissue stress should cure the bursitis.