The Vigenere Cipher is a polyalphabetic substitution cipher, which operates on a columnar transposition of the alphabet.
In order to encode the message, the Vigenere Cipher starts with a simple alphabet and adds to it depending on the key word. In this way, letter frequencies are offset from their true values in the plain text. The encrypted text can be easily decoded back to its original form by using the key word as an index.
In other words, the Vigenere Cipher is a powerful cipher that uses a key word to encrypt and decrypt information. The encryption process is simple: the user encodes text by letter so that every letter of the plaintext corresponds with a letter of the keyword in a predetermined order. A letter is encrypted by finding its position in the keyword alphabetically, adding its corresponding numerical position in the alphabet, and then substituting it with the letter found at that position in the alphabet.
The Vigenere cipher is often misattributed to Blaise de Vigenere, who was a 16th-century diplomat, but it has been used as early as 1204. A person could also create their own table to use by filling in the blank cells with words or numbers.