More definitions
...beyond the algorithms and data structures of the computation; designing and specifying the overall system structure emerges as a new kind of problem. Structural issues include gross organization and global control structure; protocols for communication, synchronization, and data access; assignment of functionality to design elements; physical distribution; composition of design elements; scaling and performance; and selection among design alternatives [Garlan and Shaw].
The structure of the components of a program/system, their interrelationships, and principles and guidelines governing their design and evolution over time [Garlan and Perry].
...an abstract system specification consisting primarily of functional components described in terms of their behaviors and interfaces and component-component interconnections [Hayes-Roth].