Lymphoid refers to something related to lymphocytes, which are a type of white blood cell that plays an important role in the immune system. Lymphoid tissue is any organ or structure where lymphocytes are found and actively functioning, such as the spleen, thymus, tonsils, and adenoids. The term "lymphoid" can also be used to describe something that has a resemblance to lymphocytes in appearance or function, for example, lymphoid follicles are structures found in certain types of tissue that have a similar appearance to lymph nodes and contain cells related to the immune system.