The acronym SOA is for Service Oriented Architecture. To define a service is simple terms , a service is a program that can be interacted with via well-defined message exchanges. Services must be designed for both availability and stability.
Service-orientation is, as per industry, the correct way to build maintainable, robust, and secure applications. When developing a service-oriented application, you decouple the service code from the technology and platform used by the client. Even securing the transfer of the message itself from the client to the service is also outside the scope of the service, and so is authenticating the caller. The service may do its own local authorization as per the requirements