What is the definition or description of: necrosis?

Dead tissue.: Necrosis is premature cell death, due to external forces acting on the cells. Causes include trauma, ischemia, toxins and infections. Since necrotic tissue has lost the ability to protect itself, it is prone to infection, and is often surgically removed, debrided, to protect neighboring living cells. Untreated, necrosis can lead to infection, gangrene, sepsis and even death.

Cell / tissue death: Necrosis is the the death of cells and tissue. In dentistry, root canals are often needed when the pulp tissue inside a tooth has gone necrotic.