WebSphere Application Server (WAS) provides the infrastructure to develop and run web and enterprise applications. It includes a web container to handle HTTP requests and servlets/JSPs, an EJB container to manage enterprise java beans, and various services like transactions, security, and messaging. WAS implements the J2EE specification and is available in different packages for single server or clustered/scalable environments. It supports the development and deployment of web services, SOA applications, and dynamic web sites.