Cervical lymph nodes are simply lymph nodes located in the neck. The medical term for the neck is cervix, though this term is rarely used.
Lymph nodes are small structures located all over the body around blood vessels and are a part of the lymph system of the body. Read more in Understanding the Lymph System.
Lymphoma is a cancer of the lymph system. It can affect any lymph nodes and cervical lymph nodes are commonly affected.