What is 'the architecture'?

While you can speak of 'the architecture' of a software system, this is typically is some n-dimensional structure, and therefore difficult to visualise. We therefore develop architecture views, that highlight some important aspect of the system, while abstracting away others. This is not a fixed set, but could be:

  • hardware & network architecture
  • physical distribution
  • functional architecture
  • software (component) architecture
  • service architecture
  • process architecture
  • colour architecture
  • system methaphore
  • protocol stack
  • visual layout

Unorthodox
This list deliverately contains some unortodox entries, but they all are relevant for some type of systems. And there will be others. And you don't have to have all of them. If the number of relevant ones exceeds five, you are dealing with a pretty complicated system. While they strictly speaking are architecture views, they by convention are often named architectures in their own right.

Primary architecture(s)
Often one architectural view will be the most defining, which you would typically mention first when introducing someone to the system, Or rather, there are two. One that gives a quick characterisation of the system, and does not need further explanation, like a web site', or 'a PSP game', or 'a car'. This architectural view is not dwelled on further when designing the system, because it is largely (assumed) understood by the audience.

No sleep till Brooklyn
And then there is the 'keeping you awake at night' architectural view, like the '99,999% availablity single shard' hardware architecture for an MMOG. Or the service archirecture defining the 2034 services for a multinational bank.