1. A collection of data units such as words, characters, or records (generally more than a single word) that are stored in adjacent physical positions in memory or on a peripheral storage device. A block can therefore be treated as a single unit whereby data can be (and usually is) transferred between storage device and memory, using one instruction. Blocks may be fixed or variable in size.
2. In coding theory, an ordered set of symbols, usually of a fixed length. The term is generally synonymous with word or string, but with the implication of fixed length.
3. See block-structured languages.
4. In parallel programming, to prevent further execution of one sequence of instructions until another sequence has done whatever is necessary to unblock it. See also blocked process.