Wiktionary
random number generator
n. A device or algorithm that generates numbers selected at random or apparently at random. In many cases they actually select successive numbers deterministically and are more technically termed pseudorandom number generator.
WordNet
random number generator
n. a routine designed to yield a random number
Usage examples of "random number generator".
The result would be controlled by a random number generator deep in the hidden layers of the operating system.
The numbers were provided on demand from a central source, accessible by WormCam, rumored to be a random number generator buried in a disused mine in Montana, based on uncrackable quantum-mechanical principles.
Descrambling the photo requires knowing the seed that started the pseudo-random number generator.