Dice roll

This is shorthand for RNG range, based on how randomness was calculated in tabletop roleplaying games.

(number of dice)d(number of sides)

The default damage range is 1d2, so that means one two-sided dice (or a coin) will be rolled/flipped. A 2d6 longsword will deal 2 rolls of a six sided dice. A steel axe with 1d6+1 damage will deal a roll of a six sided die, with 1 added to it afterwards.

Dice rolls are used for numerous mechanics aside from damage as well. These dice rolls usually have a Modifier added to the total.