htp is an HTML pre-processor. It is designed to be a flexible authoring tool that can easily be integrated into the design process.
htp works by processing special HTML files and producing as output regular HTML files ready to be served up. The original HTML files are "special" because they (possibly) contain certain markup tags only recognizable to htp. These tags are formed very similarly to standard HTML tags. This allows for an easy learning curve and the ability to use visual HTML editors to build htp files.