RNG means random number generation, the system a game uses to produce unpredictable outcomes such as loot drops, critical hits, and enemy behaviour. Players use RNG as shorthand for luck, good or bad, inside those systems.
Games cannot roll physical dice, so they generate numbers with algorithms that produce results unpredictable enough to feel random. When you attack, the game may generate a number to decide whether you land a critical hit. When an enemy falls, another number decides which item, if any, appears. The rules around those numbers are fixed and knowable, even when any single result is not.
Players talk about RNG because it explains the uneven texture of repeated play. Two players can clear the same encounter the same way and walk away with different rewards, and a run can collapse because three low probability events landed in a row. Designers tune that variance deliberately. Generous odds keep progress steady, while rare outcomes create memorable spikes and give repeated content a reason to be replayed.
Many games soften pure randomness with pity systems, weighted tables, or guaranteed rewards after a set number of attempts. Those safeguards do not remove RNG. They bound it, so bad luck has a floor and no player can fail forever at the same step.
In play"The chest is guaranteed, but the weapon inside is pure RNG."