A linear congruential generator is a method of generating a sequence of numbers that are not actually random, but share many properties with completely random numbers. These types of numbers are called pseudorandom numbers.

An LCG generates pseudorandom numbers by starting with a value called the seed, and repeatedly applying a given recurrence relation to it to create a sequence of such numbers. At a glance, the graphs will always look random (except in trivial cases, such as when the modulus is a multiple of the multiplier), but there is actually a sophisticated study of how closely pseudorandom number generators approximate processes that are truly random.