API: application programming interface.
Cocoon: Java- and XSLT-oriented publishing framework for Apache.
CSS: Cascading Stylesheet. An association of markup elements (a hyperlink, for example) with properties, often display properties (such as, “draw in blue”). Most people encounter CSSes when working with web browsers.
DOM: Document Object Model. DOM is a programming API for documents, one that emphasizes the hierarchical tree structure of XML, for example.
DTD: document type definition. A DTD is a metalanguage that defines the vocabulary of an XML document. XML Schemata do the same, in a more general framework.
FO: formatting objects. FOs describe translation of XML to presentation displays. They encapsulate layout knowledge.
FOP: formatting object to PDF (and, more generally, other presentation formats) translator.
functional programming: Lisp, Haskell and Erlang are often categorized as functional programming languages for their emphasis on immutable variables, application of side-effect-free operations, recursion and even provability. XSLT is a functional programming language, rather than a procedural one, as are C, Java, Visual Basic and so on.
HTML: HyperText Markup Language. The canonical source language for the World Wide Web.
namespace: a programming language concept to disambiguate polysemy. By recognition of the namespaces Baseball and Biology, we make it clear whether we're talking about Baseball::bat or Biology::bat. The significance for XML developers is that they can compose applications without fear that their variable and other names will accidentally collide.
SAX: Simple API for XML. An API complementary to DOM, it is event-oriented, and emphasizes a view of XML as a stream of characters.
schema: a metalanguage specification. XML Schema, for example, defines rules that constrain the contents of an XML document.
scripted document: a file that embeds both data and code to act on the data.
stylesheet: a description of a document interpretation or transformation. XSLT stylesheets are interesting for being XML documents themselves.
vocabulary: XML is actually a metalanguage in which it's possible to describe particular realizations or vocabularies appropriate to specific domains. There are XML vocabularies customized for mathematics, car sales, GNOME GUI interfaces and much more.
W3C: the World Wide Web Consortium, among other activities, publishes XML standards.
Xalan: Xalan is a Java-oriented XSLT engine maintained as part of the Apache Project.
XML: Extensible Markup Language. Think of something that looks like HTML but has enough power to encode, in principle, any digital data.
XPath: a language that addresses or identifies parts of an XML document. Think of it as a query language, complementary to XSLT (XSLTdescribes changes, XPath describes where the changes occur).
XSL: Extensible Stylesheet Language.
XSLT: Extensible Stylesheet Language for Transformations. A language specialized for mapping XML sources to other XML sources.
XSP: eXtensible Server Pages is Cocoon's mechanism for dynamic generation of XML-based web pages.