The term hit refers to an effect that applies a discrete amount of damage to a target instantaneously. The damage can be mitigated down to 0, but can never be negative. Damage dealt by hits always has one of 3 damage sources (attack, spell or secondary, but note that damage over time never hits.) and is combined of any 5 damage types (physical, fire, cold, lightning or chaos).
Besides the amount of damage, its type and source, ‘hit packages’ also contain certain mechanics and effects, such as:
and others.
Luck is a mechanic that rolls a number twice, with Lucky rolls applying the best result, and Unlucky rolls applying the worst result. Modifiers that state when Damaging refer specifically to damage ranges, and not related mechanics such as accuracy or critical strike chance.
Lucky and Unlucky modifiers affecting the same thing will cancel each other out.
Stats that state "Damage with Critical/Non-Critical Strikes are Lucky" only apply to hit damage and not ailments.
With percentage rolls, such as critical strike chance, lucky/unlucky rolls will be up to a 100% more/less modifier, changing linearly towards 0% as critical chance increases. As for damage rolls, the average damage from the roll will be at up to 33% more or less, when the minimum damage is close to zero, but will have a much weaker effect when the minimum damage is closer to the maximum.