SOAP is a protocol used for exchanging structured information between applications over the Internet. It is based on XML and is used to define messages, message envelopes, and how to process messages. SOAP uses XML to format the message, which is then sent over a network using HTTP, SMTP, or other underlying transport protocols. 

There are some important concepts and terms: 

SOAP message: A SOAP message is an XML-based message that is sent between applications using SOAP. It typically consists of a SOAP envelope, which contains a SOAP header and a SOAP body. 

SOAP envelope: A SOAP envelope is the outermost XML element of a SOAP message. It contains a SOAP header and a SOAP body, which can contain the actual message content. 

SOAP header: A SOAP header is an optional XML element within a SOAP envelope. It contains metadata about the SOAP message, such as authentication credentials, message routing information, and application-specific data. 

SOAP body: A SOAP body is an XML element within a SOAP envelope that contains the actual message content. 

SOAP endpoint: A SOAP endpoint is the URL of the service that is providing the SOAP interface.