In information technology, the term redundant has several usages:
1) Redundant describes computer or network system components, such as fans, hard disk drives, servers, operating systems, switches, and telecommunication links that are installed to back up primary resources in case they fail. A well-known example of a redundant system is the redundant array of independent disks (redundant array of independent disks).
2) Redundant information is unneeded or duplicated information.
3) Redundant bits are extra binary digits that are generated and transferred along with a data transfer to ensure that no bits were lost during the data transfer.
Redundancy is the quality of a system, an item of information, or a bit that is redundant.