What is software architecture?

A software architecture is a result of a system design which is intended for obtaining expected behivour form the system. Here the system design has to take into account the following:

• identify the subsystems which the desired system need to contain
• identify the interfaces for the above subsystems
• outline rules of interaction among these subsystems

Reference: A Concise Introduction to Software Engineering (Undergraduate Topics in Computer Science) by Pankaj Jalote, Springer-Verlag London, 2008