Lymphatic

The lymphatic system is a system of vessels and lymph nodes (plus a few organs). Its purpose is to clean up the space between your cells. After your cells take stuff it needs from blood, its "waste" comes out of the cell but not all of it goes into the blood vessels to be circulated out. The lymph, which is the "waste", is pumped out your body (Waste disposal systems) not by a central organ, but by daily movement.

Lymph nodes are found throughout the body and immune cells (mostly T, dendritic, and B cells) stop at the lymph nodes to wade around, basically just waiting around for Dendritic cells to give them something to sample. Lymph nodes are important because they are like barracks for your immune system to "get weapons" and gather "soldiers". When antigens that are identified as other get collected by the immune cells in the lymph nodes (or rather just anywhere, but lymph nodes have clusters of immune cells sticking around.), the adaptive immune system starts up.