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 It uses an unvarying transformation, that is, it uses a symmetric key They are specified elementary components in the design of many cryptographic protocols and are widely used to implement the encryption of large amounts of data, including data exchange protocols Even a secure block cipher is suitable for the encryption of only a single block of data at a time, using a fixed key A multitude of modes of operation have been designed to allow their repeated use in a secure way to achieve the security goals of confidentiality and authenticity
Block cipher - Wikipedia, the free encyclopedia