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Data Encryption Standard
DES used to be the most widely used block cipher, and it was used as an industrial standard as well. It's still popular, but it has been replaced by other advanced block ciphers in many applications. DES uses 64-bit blocks with a 64-bit key. 8 bits in the key are used as parity bits for error detection, so the key size is technically 56 bits. It's been proven to be vulnerable to brute-force attacks and some cryptanalysis attacks, which is due to its limited key size. 3DES was introduced to overcome this problem by running DES three times with different 56-bit keys. But 3DES proved to be slower than other block ciphers, such as AES.
DES uses 8 bits of the key as parity bits for error detection while transmitting or storing the keys. The bits in the 8th, 16th, 24th, ..., 64th positions are used to calculate odd parity, that is, the number of 1s in each byte of the key is odd.