What exactly does it mean to have an enlarged lymph node in your upper thigh?

Groin nodes?: There are lymph nodes in the groin whichc an enlarge for a variety of reasons such as infection of the skin of the foot or leg. In such siuations the node would be tender and then subside as the infection goes away. Painless enlargement of groin nofdes if bigger than one inch requires a medical check up to exclude any more serious cause.

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.