Bursitis is inflammation of a bursa, a lubricated pouch or sac in regions where there is a lot of movement between muscles and bone.

Carpet fitter's knee - knee problems may include infrapatellar bursitis.

Housemaid's knee - pre-patellar bursitis.
Common types of bursitis
Most cases of bursitis are of the non-infected type, and resolve on their own. The most common bursitis in the knee is pre-patellar bursitis, often seen in someone who has done uncommon exercise while kneeling, such as scrubbing a floor or fitting floor tiles. If there is any penetration of the bursa then it may become infected. Pes anserine bursitis may ocur in breaststroke swimmers.
CLINICAL PUBLICATIONS
Endoscopic treatment of prepatellar bursitis. Huang Y-C and Yeh W-L. Int Orthop. 2011 Mar; 35(3): 355–358.
Management and outcome of infective prepatellar bursitis. Wilson-MacDonald J. Postgrad Med J. 1987 Oct; 63(744): 851–853.
Prevalence of knee bursitis in the workforce. Le Manac'h AP, Ha C, Descatha A, Imbernon E and Roquelaure Y. Occup Med (Lond). 2012 Dec;62(8):658-60.