A service-oriented architecture (SOA) is a style of design that guides all aspects of creating and using business services throughout their lifecycle (from conception to retirement), as well as defining and provisioning the IT infrastructure that allows different applications to exchange data and participate in business processes regardless of the operating systems or programming languages underlying those applications.

Simply put, SOA is a system architecture based on services. Although older styles of SOAs include those that use DCOM or CORBA, today when people speak of SOAs, they mean SOAs based on web services and the standards that go along with them.