Pseudorandomness

Pseudorandomness: the act of being "almost random"

A pseudo-random variable is a variable which is created by a deterministic procedures 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.

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

See also Random Variable, Extractor, Disperser, Expander.