Refers to Session EnterpriseJavaBeans that maintain no conversational state with the client. Since StatelessSessionBeans have no state (per client), each of them are essentially identical so a small pool of identical StatelessSessionBeans can be used to service a large number of clients.
Contrast with StatefulSessionBean? and EntityBean.
Prior to the advent of the EnterpriseJavaBeans 3.0 spec, many people considered that StatelessSessionBeans were the most appropriate use of EJB technology, with StatefulSessionBeans carrying state (better held in the client) and EntityBean better replaced with by an ObjectRelationalMapping technology, such as hibernate. -- PaulBrowne