Here is the simple explanation of SOA (Service Oriented Architecture) with technical touch by Uncle Bob.
SOA is very obscure, if not obliterate, term - one of many which are humming on the web. Thanks to guys like Martin, who tries to address the real side of it. Read more here. I recommend reading this post, and upcoming posts, before you start speaking about SOA in any conference or technical discussions. Well the same is true for every other Buzz word.
SOA is the practice of sequestering the core business functions into independent services that don’t change frequently. These services are glorified functions that are called by one or more presentation programs. The presentation programs are volatile bits of software that present data to, and accept data from, various users.