1. The spread of a cancer from the original tumor to other parts of the body: Dr. Smith explained Tom's case of cancer as resembling tiny clumps of cells which had been transported by his blood or lymph to a further organ of his body.
2. A malignant tumor that has developed in the body as a result of the spread of cancer cells from the original tumor: A tumor formed by cells that have spread is called a "metastatic tumor" or a metastasis which contains cells that are like those in the original or primary tumor.

3. Etymology: from Greek metastasis, "transference, removal, change"; from methistanai, "to remove, to change", from meta-, "over, across" + histanai, "to place, to cause to stand".

It was a rhetorical term in Late Latin for "a sudden transition in subjects"; the medical use for "shift of disease from one part of the body to another" dates from 1663 in English.