The document that is used by XSLT to indicate, how to transform the elements of the XML document to another format is
ans is C style sheet
under XSLT, a XSLT stylesheet is used to describe transformation rules in XML format. This is read by an application called an "XSLT Processor," transforming a designated XML document. The transformation results are output in XML, HTML or text format.
refer http://www.xmlmaster.org/en/article/d01/c07/