The Data Encryption Standard, or DES for short, is a symmetric-key block cipher designed by IBM and published by the National Institute of Standards and Technology (NIST). The plaintext is broken into blocks of 64-bits and encryption is performed block-wise. This means that the cryptographic key and the algorithm are applied to it together rather than one bit at a time. The encryption process consists of 16 rounds and each block is encrypted using a key to a cipher-text (64-bits) by using permutations and combinations. They key used in DES has 56-bits as a functional key while the rest 8 bits are for parity checking.
DES was actually the first encryption algorithm approved by the US government for public disclosure. It is now insecure due to its small key size – it is vulnerable to a brute force attack.
For more details check the FAQ for this algorithm.