Numerous service models have been proposed in the form of ”as a Service” or ”aaS” in the past. This is especially eminent in the era of the Cloud under the term of anything as a service or everything as a service(XaaS). A unified view of XaaS can aid efficient classification of services for service registration, discovery, and composition. In view of that there lacks such a unified view which is demanded by systematic application of XaaS in the Web Service Ecosystem, towards proposing a taxonomy of ”aaS”, we present in this work a collection of ”aaS” based on a throughout literature survey. We also proposed a strategy to identify the terms from the servicelization perspective.