What does itmean when lymph glands on a chest xray are enlarged?

Many things: Inflammation of the lymph nodes (infection, cancer etc) and lead to enlargement of the nodes and their appearance on xray see your doctor.

Infection/tumor: Lymph nodes in mediastinum of chest can enlarge with reaction to infections such as TB , histoplasmosis, and coccidiodomycosis. Sometimes bacterial infections in lungs demonstrate reactive lymph nodes. Lymph nodes can also enlarge with tumors such as lymphoma.