A block is a contiguous set of bits or bytes that forms an identifiable unit of data. The term is used in database management, word processing, and network communication.
1) In some databases, a block is the smallest amount of data that a program can request. It is a multiple of an operating system block, which is the smallest amount of data that can be retrieved from storage or memory. Multiple blocks in a database comprise an extent.
2) In word processing, a block is a contiguous set of characters. Often it consists of a phrase, a sentence, a paragraph, or a set of paragraphs that is selected by the user for copying/pasting, cutting, or moving. But a block can consist of any contiguous set of characters, whether or not it forms a logical unit of text.
3) In network communication, a block is a group of data bits or bytes that is transferred as a standard unit. The size (or length) of such a block depends on the communications protocol.