The SEI has compiled a list of modern, classic, and bibliographic definitions of software architecture.
Modern definitions are definitions from Software Architecture in Practice and from ANSI/IEEE Std 1471-2000, Recommended Practice for Architectural Description of Software-Intensive Systems.
Classic definitions appear in some of the more prominent or influential books and papers on architecture.
Bibliographic definitions are taken from papers and articles in our software architecture bibliography.
As part of this effort, we are interested in how our visitors define software architecture. We have collected several hundred community definitions.