RNG
Also said as Random number generator, PRNG, Luck
The part of a game that makes up random numbers. It is really a formula that produces a long list that only looks random, starting from one number called a seed, so the same seed always gives the same list.
Randomness makes each attempt different and lets a weaker player win sometimes. A saved seed also lets you replay a run, test a bug, or share a world, and it stops players reloading until they get lucky.
Say it
“Use a seeded generator and store the seed in the save, so reloading can't re-roll a shot. Log the seed with every bug report so we can replay what happened.”
Where you’ve seen it
XCOM: Enemy Unknown saves its random seed, so reloading and taking the same shot gives you the same miss. Enemy Within added a Save Scum option for people who want a fresh roll each time.
Not to be confused with procedural generation
RNG only hands out numbers. Procedural generation is what you build from them: maps, loot, names.