1. A malignant tumor originating in a lymph node; such as, Hodgkin's disease or any of the range of cancers known as non-Hodgkin's lymphomas.
2. Any of various usually malignant tumors that arise in the lymph nodes or in other lymphoid tissue.
3. Any neoplastic disorder of lymphoid tissue; the term is often limited to the malignant lymphomas.
4. A tumor arising from any of the cellular elements of lymph nodes.

Lymphoma is a cancer of a class of cells called lymphocytes which are key players in the normal immune response.

This means that lymphoma, together with the leukemias and multiple myeloma, is unusual among cancers in that it represents a malignancy of the immune system; the very system of the body that is supposed to protect and defend our bodies from infection and, some believe, from cancer.

It is significant to know that the term lymphoma actually encompasses a group of diseases. This means that the best therapy for one person may be very different from the best therapy for someone else with a different form of lymphoma. The causes of lymphoma remains largely unknown.

A premalignant lymphoma in which the lymph nodes show enlarged follicles composed predominantly of closely packed, large reticuloendothelial cells.