What exactly does it mean when your lymph nodes are swollen?

Monitoring Centers: The lymphatic system absorbs and carries things too big to go into the arteries and veins like bacteria eaten by white cells and digested food. A lymph node "tastes" the lymph to see if anything bad is there like bacteria, viruses, cancers, etc. When it detects a problem, it alerts the immune system and enlarges in response to the inflammation they create when they react. You can feel them then.