A Transposition Cipher is a method of encryption that rearranges the letters of a message to create a coded version. Instead of changing the letters themselves, it alters their positions based on a specific system or key. This means that the original message can be reconstructed if the correct method is known. In a typical transposition cipher, the plaintext is written out in rows and then read out in a different order, such as by columns. This technique can be applied in various ways, including the use of rail fence ciphers or columnar transposition. The security of the cipher relies on the complexity of the rearrangement method used.