It may be a lymph node, here's some info.
3. Lymph Nodes
At several sites in the human body, the lymphatics join to form a bundle of tissue called lymph nodes, or popularly known as lymph glands. The term "lymph gland" technically is not accurate because "glands" make hormones, and "lymph glands" do not manufacture hormones.
Any fluid that enters the lymphatic system must pass through at least one lymph node before advancing to the heart and reentering the circulartory system.
The individual nodes vary in size from microscopic to approximately 2.5 cm [1 inch] in diameter. Each node consists of a tightly packed mass of white blood cells forming lymphoid tissue. In the node, several small lymphatic vessels convey lymph to the node filter and then to a single larger vessel that carries the fluid out of the node. Every lymph node has its own small artery and vein.
There are approximately 600 lymph nodes in the human lymph system. The nodes generally occur in clusters, particularly under the armpits, behind the ears, in the groin, in the abdominal cavity, behind the knees, and in other areas.
Lymphoid tissue in the nodes produce antibodies and hold reservoirs of lymphocytes, as discussed below. Lymph nodes also contain macrophages, which are large cells that engulf bacteria and other foreign particles. Thus, lymph nodes function as filters that trap cancer cells, bacteria, and viruses.
Lymph nodes play an important role in fighting infection, primarily in their roles in antibody production and lymphocyte storage.