What?
Software architecture encompasses the following:
Rational Unified Process, The: An IntroductionAddison-Wesley, 2003

  - Significant decisions about the organization of a system

  - Selection of structural elements and their interfaces, by which the system is composed together with their behaviour as specified in the collaboration among those elements

  - The composition of those elements into progressively larger subsystems, the architectural style that guides this organisation, these elements and their interfaces, their collaborations and their composition.