Neoplasm

A neoplasm is tissue that is growing where it should not be. If they become a mass, they become a tumour. Tumours are either malignant (harmful) or benign (safe). Cancer, for example is malignant and sometimes spreads to other places on the body. Some tumours have a cause that makes them grow. For some tumours no cause is known.^[1][2][3] A tumour usually forms as a lump or mass.^[4]

The Simple English Wiktionary has a definition for: tumor and tumour.

Tumours can occur in humans and animals. In humans, tumors can occur because the genetic code of cells is modified too much, causing affected cells to divide and expand uncontrollably.^[5] The Tasmanian Devils in Tasmania, Australia are in danger of becoming extinct because of a malignant tumour that grows on their face.^[6]