Roe and caviar basically refer to the same thing: fish eggs. However, the term roe refers to the fish eggs (or male fish sperm) themselves while caviar is roe that has been salted or “cured” and then placed in tins for storage and aging.
While I detest Beluga caviar, and have limited appreciation for Salmon roe, I was raised on Herring roe, and highly recommend it. It's crunchy, not mushy, fresh flavored and not fishy at all, and it's one of the highest nutrient dense foods in the known universe.
Thank you Master @quochuy, I will try to remember say this, if my Master ever catches me serving him roe.