I only learned what "rounds" and "grand rounds" exactly were when I started my residency two months ago.
Grand rounds in our department are once a week and are described as "where Oral Surgery residents cry." The OMS residents have to present cases where they participated in the surgery and treatment of the patient. They present the pre-op pictures, films, history and background, surgical pictures, post-op, etc. But they don't just present, the OMS attendings are all sitting in the front waiting to rip the residents apart for every detail they present and sometimes their questions are just ridiculous (like they have no learning value at all). For example, one week one of the attendings asked the resident "If you only had one hand, how would you go about performing this procedure?" Sometimes the cases they present have to follow a theme, like pathology or orthognathic.
Rounds are every morning and evening. It is when the OMS residents and GPR residents go to the patients who are staying in the hospital overnight after their oral surgeries. The residents do exams and check the patients to make sure they are doing well after the surgery or to see if any problems complications are developing.