(n.) (1) In word processing, a block is a group of characters that you have marked to perform some action on them. For example, to move a section of text, you must first block it. This is sometimes called a block move.
To specify a block of text, you press special function keys (or click with a mouse) at the beginning and end of the block. The function keys differ from one word processor to another. Word processors usually display blocks by highlighting them on the screen.
(3) In network communications, a block is a fixed-size unit of data that is transferred together. For example, the Xmodem protocol transfers blocks of 128 bytes. In general, the larger the block size, the faster the data transfer rate.