The extension .XSD refers to files of the type, XML schema definition. This is a kind of configuration file that stores information regarding the contents of an xml file.

As we know, the XML files are used for document structuring and the Schema design needs to be stored somewhere. The XML SD (schema definition) files take care of this operation so that the interpreter on the client side can know the meaning of each of the tags inside the actual XML file. The XSD file defines the relationship between the elements of the xml file and uses the standards specified by W3C for the same.