A symmetric block-cipher algorithm with a 128-bit block size, and key sizes up to 256 bits.
Twofish is a symmetric block-cipher algorithm with a 128-bit block size, and key sizes up to 256 bits.
The Twofish block-cipher was one of the five finalists of the Advanced Encryption Standard contest, but was not selected. It is related to the earlier Blowfish block-cipher.
See the wikipedia page for more information.