Savage Attacks is a passive feature available to Half-Orc characters. When they score a critical hit with a melee weapon attack, they can roll one of the weapon’s damage dice one additional time and add it to the extra damage of the critical hit.
The description of this racial trait in game (last update v4.1.1) is very poorly worded. While it states that damage dice are "tripled", this is only true when rolling a single base dice (e.g. 1d6) that would gets doubled on a normal critical hit without this feature (2d6) or tripled on a critical hit with this feature applied (3d6). In every other case, the actual result is the doubling of whatever original damage dices applied, as for any normal critical hit, and then the addition of a single additional damage dice. For example, a greatsword hit deals 2d6 base damage, gets normally upgraded to 4d6 (2x 2d6) damage with a normal critical hit, and gets upgraded to 5d6 (2x 2d6 + 1d6) with a critical it using this feature.
This feature also adds one dice on critical hits performed using the paladin smite ability. This means that a critical hit with smite activated will get a total of two additional dices. This seems to be linked to the fact that the smite damage seems to be computed separately from the base attack. Other sources of additional damage dices such as elemental enchantments on weapons, sneak attack dices, battle master superiority dices, are accounted for in the calculation of the original attack and do not cause this feature to add more damage dices like smite does.
This feature does not work at all with unarmed attacks or wildshape animal attacks.