Blocks are visualization of core system elements (or set of elements) responsible for the performance of a particular task.

The primary usage of block diagrams

Block diagrams are used for higher-level, less detailed descriptions to clarify overall concepts in a readable, graphical format rather than implement them in practice.

The components of the block diagram

The structure and flows within blocks are described with OMG Systems Modelling Language (SysML), which provides a simple explanation of the relations between components, the type of data they consumed, and their flow direction.