It is a method of encrypting alphabetic text by using a form of polyalphabetic substitution. A polyalphabetic cipher is any cipher based on substitution, ie using multiple substitution of alphabets. The encryption is done using a Vigenère table.
To encrypt a message using the Vigenère Cipher you choose a keyphrase. Then repeat this keyword over and over until it is the same length as the original text; this is referred to as a keystream.
