Used in cryptography to ensure that an encryption mechanism, such as a stream cipher or a block cipher in a streaming mode, generates a unique stream that is independent of all other streams encrypted with the same key without reapplying the (computationally expensive) cryptographic keying process. The Initialization Vector must be known by the receiver and can be exchanged as part of the session setup or transmitted independently.
Ferguson, N, Schneier, B. Practical Cryptography. New York, NY: John Wiley & Sons, 2003.