J-SOAP11 is a Java-based implementation of the SOAP (Simple Object Access Protocol) 1.1 specification, which is used for exchanging structured information in web services. It provides a framework for creating, sending, and receiving SOAP messages, enabling communication between different systems over the internet. J-SOAP11 simplifies the process of building SOAP-compliant web services in Java applications and supports various features such as serialization, deserialization, and handling of SOAP envelopes.