The Data Encryption Standard (DES) is a symmetric key encryption algorithm that uses a 56-bit key to encrypt and decrypt data. It operates on 64-bit blocks of data and uses a complex set of permutations and substitutions to produce the ciphertext. DES uses a Feistel structure, where the input block is divided into two halves and each half undergoes a series of transformations before being combined again. Despite being widely used in the past, DES is no longer considered secure due to its small key size and vulnerabilities to various attacks. Its successor, the Advanced Encryption Standard (AES), is now the recommended encryption standard.