What is granuloma?

Small nodule: Doctors use the word "granuloma" in different ways. Pathologists may be the most precise in their use. It's basically a collection immune cells (macrophages) that are in a tight knit ball - could be either from an infection or not. There may be some necrosis in the granuloma.

Angry macrophages: The macrophages (monocytes in the tissue) stick together in a reaction, typically to wall something off (in health -- splinter, suture, or walling off TB or fungus); they may do so without a good reason in illness (crohn's, sarcoid, many others). A radiologist may see a lesion on chest x-ray and be fairly certain it is a granuloma.