What do hard, swollen, extremely painful/tender lymph nodes in the neck mean?

Diff possibilities. Tender is usually a good sign & if you have a few relatively small tender lymph nodes & you struggle with allergies or have a cold, those could cause it. However if you have a very lg or hard, immobile node(s) it's best to get that checked out. You might also want to check for swollen lymph nodes elsewhere in the body & if you find some, that would be another reason to get checked out.
Monitoring Centers. Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria, viruses, cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.

Related Questions

What to do about swollen, hard, tender lymph nodes in my neck that do not move?

See your doctor. Lymph node swelling that is tender may indicate an infection of your teeth, mouth, etc. A doctor is the best person to determine if the lymph glands are swollen from an infection or another process. Read more...

What can I do about swollen, hard, tender lymph nodes in my neck that do not move?

How long? How long have you have those nodes? If they are recent and occured with an infection, they will resolve on their own, if they have been there for a while, they need to be checked by your doctor. Read more...