Jtpl is a template engine for Java Servlet which allows you to store your HTML code apart from your Java code.
A template engine is a software module which is used to generate HTML pages. The layout of a HTML page is defined within a template file, which can be designed by using a standard HTML editor. At run-time, the application program instructs the template engine to load the template, fill in variable values, repeat blocks and produce the final HTML page.
There are other template engines (like Velocity, WebMacro or Struts) which are huge and use complex template syntaxes.