Block

1. A group of bits or digits that is transmitted as a unit and that may be encoded for error-control purposes.

2. A string of records, words, or characters, that for technical or logical purposes are treated as a unit.

Note 1: Blocks (a) are separated by interblock gaps, (b) are delimited by an end-of-block signal, and (c) may contain one or more records.

Note 2: A block is usually subjected to some type of block processing, such as multidimensional parity checking, associated with it.

3. In programming languages, a subdivision of a program that serves to group related statements, delimit routines, specify storage allocation, delineate the applicability of labels, or segment parts of the program for other purposes.

Source: from Federal Standard 1037C and from MIL-STD-188

In the construction (building) industry, a block is a shaped piece of masonry.