Pseudorandom ensemble

Let $U = \{U_n\}_{n \in \mathbb{N}}$ be a uniform ensemble and $X = \{X_n\}_{n \in \mathbb{N}}$ be an ensemble. The ensemble $X$ is called pseudorandom if $X$ and $U$ are indistinguishable in polynomial time.

References

Goldreich, Oded (2001). Foundations of Cryptography: Volume 1, Basic Tools. Cambridge University Press. ISBN 0-521-79172-3. Fragments available at the author's web site.