Service-Oriented Architecture
Here's a definition I tend to use:
Service oriented architecture (SOA) is an architectural style that supports service orientation. SOA can be applied by an organization to both its business model and its IT. Applied to the business model, SOA structures the business' activities as repeatable processes and reusable services. Applied to IT, SOA structures applications as repeatable processes and reusable services. The processes and services implemented in a business' IT should have a one-to-one correspondence to those in the business' model. Structuring a business model and its IT to follow the same SOA enables IT to more effectively support and automate the business' operations, and enables the business to be more flexible and respond more rapidly and more easily to changes in the business' environment.
Service-oriented architecture
(SOA) is an architecture for business applications composed of a loosely coupled collection of business services. See the developerWorks SOA and Web services and Architecture zones, especially "What is SOA?"
An important part of an SOA is an enterprise service bus (ESB).
Terminology
Some common SOA terminology:
Standardization
There's an effort to develop open standards for SOA. It's being lead by the Open Service-Oriented Architecture (OSOA) organization, which is developing the Service Component Architecture (SCA) and Service Data Objects (SDO) specifications into standards. Meanwhile, the Apache Tuscany project is developing open source implementations of the specs.
Miscellaneous
I discuss some of the fundemental value proposition of SOA in Back to Basics on SOA with Bobby Woolf.
A related technology is Event-Driven Architecture.
