XSLT (Extensible Stylesheet Language Transformations) is a language for transforming XML documents into other XML documents, or other formats such as HTML for web pages, plain text or XSL Formatting Objects, which may subsequently be converted to PDF, PostScript and many other formats.
XSLT is designed for use as part of XSL, which is a larger specification that combines XSLT with an XML grammar for XSLT stylesheets, and the XML Path Language (XPath), which is used for addressing parts of an XML document.
XSLT is a Turing-complete language, meaning that it can be used to write programs that transform XML documents in any way that can be expressed as a set of rules.
In addition to its use as part of XSL, XSLT is also used by many web browsers as a way to transform web pages from their XML source documents into HTML.
XSLT is also used by many programming languages as a way to enable the processing of XML documents. For example, PHP has an XSLT extension that allows PHP programs to transform XML documents.