The goal of XSL has evolved over time. Today, XSL is a blanket term for a number of derived technologies that altogether better qualify and implement the original idea of styling XML documents. The various components that fall under the umbrella of XSL are the actual software entities that you use in your code:
Rule-based language for transforming XML documents into any other text-based format. XSLT provides for XML-to-XML transformation, which mostly means schema transformation. An XSLT program is a generic set of transformation rules whose output can be any text-based language, including HTML, Rich Text Format (RTF), and Wireless Markup Language (WML), to name just a few.
Query language that XSLT programs ...