An entity relationship diagram (ERD), one instance of a block structure, represents an information system by showing the relationships between people, objects, locations, events or theories within that system. (See a picture over the ERD definition page.)
Block diagrams are used heavily in engineering and design of diagrams including processes, hardware, software and electronics. Most commonly, they signify theories and systems at a higher degree, less thorough overview. The diagrams are useful for troubleshooting technical issues.
The simplification in block diagrams may also be helpful when demonstrating an idea, but hiding the inner workings of potentially secret intellectual property (IP). Top-down layout in electrical engineering frequently progresses through progressively detailed block diagrams. Block diagrams in procedure control show the functions of surgeries but not the components that play them. The functions of block diagrams can then be implemented with programmable logic controls (PLC).
Contrary to schematics, blueprints and layout diagrams, block diagrams don't portray the necessary detail for physical structure. Block diagrams are made simple in order to not cloud theories.
Block diagrams can also be used in a scientific context. In the analysis of math, for instance, block diagrams can be used to show biological functions and interrelations.