A web container handles requests for servlets, JSP files, and other types of server-side include coding. The web container creates servlet instances, loads and unloads servlets, creates and manages request and response objects, and performs other tasks for managing servlets effectively.
In the WebSphere administrative domain, each application server contains zero or one web containers. The Web server plug-ins provided by the WebSphere Application Server product help supported Web servers pass servlet requests to web containers.
"Servlet engine" is an older (Version 3.5.x) name for a Web container, and represents the same functionality.