Is leukemia a form of cancer?

Yes. Yes. Leukemia is a cancer of the white blood cells. Leuk = white -emia = blood general divisions are: acute (a) vs. Chronic (c) lymphoid (l) vs. Myeloid (m) giving the main leukemia types - aml, all, cml, cll.
Yes. Leukemia is a blood cancer which starts in the cells in the bone marrow. These cells usually grow and mature in the bone marrow and then enter the blood stream where they help fight infection, supply blood to carry oxygen and platelets to control bleeding. When one of these cell types becomes cancerous, they may be present in large number in the blood or bone marrow and it is called leukemia.