Which term refers to an increase in the number of cells in a tissue or organ?

The term that refers to an increase in the number of cells in a tissue or organ is hyperplasia. This process leads to the enlargement of an organ or tissue due to cell proliferation. Hyperplasia can occur as a normal physiological response to various stimuli, such as hormonal changes or tissue repair, and can also be associated with pathological conditions.

In contrast, an embolus is a foreign body that travels through the bloodstream and can obstruct a blood vessel, but it does not refer to cell proliferation. Plethora typically refers to an excess of bodily fluids or blood in certain areas, which is unrelated to cell count. Circulatory shock is a medical condition characterized by inadequate blood flow to the tissues, leading to organ dysfunction, and does not concern cellular proliferation either. Understanding hyperplasia is crucial in pathology as it helps recognize and differentiate between normal adaptive changes and disease processes.