In layman's terms, REST is the rules that are used for creating a web service. REST is Representational State Transfers. A type of software design where services are provided to other components in a network, using system protocols, to communicate what services need to be performed and where. SoapUI is an online testing program used on SOA and REST.
When SoapUI tests either an SOA or a REST it's looking at functionality, doing a general evaluation and how to increase the overall efficiency of what is being tested. Open source cross-platform testing for APIs
