What is the definition or description of: biopsy?

Tissue sample: Biopsy is tissue removed by needle or cutting to remove part of a body part. It is usually a small amount of material that is processed by a pathologist. Most of the time it is stained and looked at through a microscope to arrive at a diagnosis. Special processes are done for some tissues or problems. The purpose is to tell what the problem is (diagnosis). This can guide treatment.