What does it mean if a physician is fellowship trained?

Fellowship training is additional training done by a physician after completing their residency. It provides focused training in a specific aspect of medicine/surgery. For example, I completed my five year urology residency then did an additional year of training in robotic and laparoscopic surgery in Seattle. During this year, I took part in over 300 robotic surgeries. 

The literature also suggests better surgical outcomes with a fellowship trained urologist.  See the below links for examples: