A stencil is any text FILE that contains special tags understood by CStencil Class (used to parse a stencil and generate a text stream by replacing elements found within the stencil by output generated by an object implementing the ITagReplacer INTERFACE) or a derived class.
A SRF is a stencil containing tags understood by CHtmlStencil.
The stencil processor is a FEATURE which allows content generation based on the stencil SRF files.
It allows separating the static PART of the response from dynamic content.