Architecture is an uncertain term. The broadest meaning of architecture I’ve heard is “everything that is important”.
Martin Fowler in “Patterns of Enterprise Application Architecture” writes:
“The software industry delights in taking words and stretching them into a myriad of subtly contradictory meanings. One of the biggest sufferers is “architecture.” I tend to look at “architecture” as one of those impressive-sounding words, used primarily to indicate that we’re talking something that’s important. But I’m pragmatic enough not to let my cynicism get in the way of attracting people to my book. 
“Architecture” is a term that lots of people try to define, with little agreement. There are two common elements: One is the highest-level breakdown of a system into its parts; the other, decisions that are hard to change. It’s also increasingly realized that there isn’t just one way to state a system’s architecture; rather, there are multiple architectures in a system, and the view of what is architecturally significant is one that can change over a system’s lifetime.”
There are also more accurate definitions in international standards.
ANSI/IEEE Std 1471-2000, Recommended Practice for Architectural Description of Software-Intensive Systems:
“Architecture is defined by the recommended practice as the fundamental organization of a system, embodied in its components, their relationships to each other and the environment, and the principles governing its design and evolution.”
ISO/IEC 42010 (international standard for architecture descriptions of software-intensive systems):
“Architecture (of a system): fundamental concepts or properties of a system in its environment embodied in its elements, relationships, and in the principles of its design and evolution.”
