A neoplasm is an abnormal growth or tumor that occurs when cells in a part of the body begin to reproduce and grow uncontrollably. This term refers specifically to any new, benign (non-cancerous) or malignant (cancerous) tissue that forms as a result of this uncontrolled cell division. Neoplasms can be classified according to their level of differentiation - the extent to which they resemble normal cells in terms of structure and function.