Luck influences everything in the game that is chance related, from evading attacks and afflictions, to scoring critical hits, determining the final damage between a "min-max" range, performing successful stealth or detection actions, haggling with NPCs, and so on. Every time a chance is "rolled", that chance is biased by the creature’s luck, which can either be positive (better chances), or negative (worse chances), and ranges between -1000 and +1000. Luck is determined by a creature’s Charisma.
Base = 0 for Human players, but can vary depending on creature type.
Bonus depends on the creature's Charisma:
Assuming a random roll with a certain Chance to succeed (e.g. 25%, represented as 0.25), Biased Chance is the actual success chance altered by the player's Luck.