This document discusses Java Server Pages (JSP) engines and how they work. It explains that JSP engines allow web servers to process JSP pages by converting JSP code and elements into servlets. When a request comes in for a JSP page, the web server forwards it to the JSP engine. The JSP engine compiles the page into a servlet class, executes it, and returns the dynamic HTML output to the web server as an HTTP response to the client. This allows JSP to generate dynamic web pages using Java code for better portability compared to technologies like ASP.