CBC stands for Cipher block chaining, its mode is defined for the block cipher algorithm. Block cipher occurs when you have a sequence of bits that are encrypted as a block with a cipher key applied to the whole block. It’s preferred because it uses a chaining technique that causes the decryption of a block of ciphertext to be dependent on the preceding ciphertext blocks. Any changes or rearrangement of the ciphertext blocks also causes the decryption of the blocks to become corrupted.