Original: In cryptography, RC4 (also known as ARC4 or ARCFOUR meaning Alleged RC4, see below) is the most widely-used software stream cipher and is used in popular protocols such as Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks).
Simplified: In cryptography, RC4 (also known as ARC4 or ARCFOUR meaning Alleged RC4, see below) is one of the most common software stream cipher. It is used in popular protocols like Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks).