Answer Description
A block cipher encrypts data into fixed-length groups of bits, called a block. In this question, the cipher is transmitting the data one block at a time.
Wikipedia
In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called blocks, with an unvarying transformation that is specified by a symmetric key Block ciphers operate as important elementary components in the design of many cryptographic protocols, and are widely used to implement encryption of bulk data Even a secure block cipher is suitable only for the encryption of a single block under a fixed key A multitude of modes of operation have been designed to allow their repeated use in a secure way, commonly to achieve the security goals of confidentiality and authenticity However, block ciphers may also feature as building blocks in other cryptographic protocols, such as universal hash functions and pseudo-random number generators
Block cipher - Wikipedia, the free encyclopedia