Jeremy Crawford clarified it on his twitter https://twitter.com/JeremyECrawford/status/688426292077658112?ref_src=twsrc^tfwWhere is that in the PHB?
Where is that in the PHB?
Savage Attacks. When you score a critical hit with a melee weapon attack, you can roll one of the weapon’s damage dice one additional time and add it to the extra dam age of the critical hit.
It tends to make me want a Great-Axe, not a Greatsword, since 3d12 is better than 5d6, at least in this player's mind! I felt that was a nice, subtle nudge towards using an axe as a HalfOrc, which I liked.