Pseudorandomness

Pseudorandomness: the state of being, while statistically seemingly random, generated at least in part by a definite computational process. "Almost random"

A pseudo-random variable is a variable which is created by a deterministic procedure which takes random bits as input. The pseudo-random string will typically be longer than the original random string but less random. This can be useful for randomized algorithms.

Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin. - John von Neumann (1951)

(There are much better introductions out there. Please fix the above)

See also Random Variable, Extractor, Disperser, Expander.