XSLT stands for "Extensible Stylesheet Language Transformations."
XSLT is a language commonly used, among other things, for transforming XML documents into HTML or XHTML documents in order to create web pages. Normally, each XML element is converted into an (X)HTML element. XSLT relies on XPath technology to identify individual nodes in the XML document in order to convert these elements.
Since the Whitman Archive mainly works with documents encoded in XML, we need XSLT to transform the data from these XML files into XHTML documents that can be easily read and displayed by a browser.