The Vigenère Cipher is a method of encrypting alphabetic text by using a simple form of polyalphabetic substitution. It employs a keyword, where each letter of the keyword corresponds to a shift in the alphabet for the letters of the plaintext. For example, if the keyword is "KEY" and the plaintext is "HELLO," the first letter of the keyword shifts the first letter of the plaintext, the second letter shifts the second letter, and so on. This cipher is more secure than a simple Caesar Cipher because it uses multiple shifts based on the keyword, making it harder to break. However, it can still be vulnerable to frequency analysis if the keyword is short or if the same keyword is used repeatedly. The Vigenère Cipher was widely used in the 19th century and remains a classic example of encryption techniques.