Original: Bubonic plague was often used synonymously for plague, but it does in fact refer specifically to an infection that enters through the skin and travels through the lymphatics, as is often seen in flea-borne infections.
Simplified: Bubonic plague is the best-known form of the disease plague, which is caused by the bacterium Yersinia pestis. The name bubonic plague is specific for this form of the disease, which enters through the skin, and travels through the lymphatic system.