SOA is an approach for linking resources to obtain or present data on an “on demand’ basis. It is a data access and delivery strategy pursued by the enterprise — it is not simply a tactic or technique that the enterprise adopts to pursue a goal of improved application interfacing.
Service Oriented Architecture (SOA), is an approach for building computing applications that support or automate business processes by using a set of loosely coupled black‐box components. SOA represents a dramatic change in the relationship between business and IT.
SOA makes technology a true business enabler and empowers business and technology leaders alike. From a technical perspective, SOA is a method to design and architect solutions. It could be implemented in a messaging or integration layer or it could be a way that an application is designed to provide services to other applications.
Source: Guide to the Business Process Management Body of Knowledge – ABPMP BPM CBOK V3.0.