What is "replay attack"

n. (context computer science security English) An attempt to subvert security by recording legitimate communications and repeating them to try to impersonate a valid user.

A replay attack (also known as playback attack) is a form of network attack in which a valid data transmission is maliciously or fraudulently repeated or delayed. This is carried out either by the originator or by an adversary who intercepts the data and re-transmits it, possibly as part of a masquerade attack by IP packet substitution.