What are RNGs ?

A random number generator (RNG) is a technology or device that generates a sequence of numbers or symbols that does not have a pattern and cannot be reasonably predicted better than by a random chance. Random number generators can be true hardware random-number generators (HRNG), which generate genuinely random numbers, or pseudo-random number generators (PRNG) which generate numbers which look random, but are actually deterministic, and can be reproduced if the state of the PRNG is known.