In Pokemon, there are lots of random events that occur:
However computers and consoles can’t create random numbers, they can only generate random-looking numbers using an algorithm.
Since algorithms are repeatable, if we know the algorithms the game uses to generate pseudorandom numbers we can recreate them on our computers.
In this way, we know exactly when to carry out an action (such as pressing the ‘A’ button) to start a Pokemon battle and get the exact results we want.
RNG abuse is the process by which we abuse these game mechanics to encounter any wild Pokemon, a legendary with any stats, or even breed a shiny Pokemon at the press of a button.