Introduced in 1998, 3DES, also known as Triple DES, Triple DEA, TDEA, or the Triple Data Encryption Algorithm, is a cryptographic cipher. It is a symmetric key block cipher, meaning that the same key is used to encrypt and decrypt data in fixed-length groups of bits called blocks.
It is called "Triple DES" because it applies the DES cipher three times when encrypting data. When DES was originally developed in 1976, it used a key size of 56 bits, which was a sufficient level of security to resist brute-force attacks. Since then, computers have become cheaper and more powerful, enabling the 3DES algorithm to apply DES three times consecutively, essentially stopping brute-force on modern computers.