Service Oriented Architecture (SOA) describes an IT infrastructure which allows varying applications to exchange data with one another, whilst they work together as part of a whole business process.
SOA separates organisational functions into distinct units or services which are then made accessible over one unique, singular network. SOAs build applications out of software services and building an architecture to connect these services seamlessly together.
SOA is typically based on web service standards, but the services do not have to be online. Software services can be from on-site software, on-demand hosted services, or a mixture of the two. For example, an SOA application could incorporate both an on-site stock tracking service and a hosted payment gateway service into a single point-of-sale application.