"Rendering" is the technical term for creating a graphical display.
In low-level graphics APIs, the rendering function is done by calling functions that draw lines and boxes and bitmaps and stuff.
For a web page, that's not possible, so in JSP terms, rendering refers to generation of the raw HTML tags and text that will be used to draw the web page.
Education won't help those who are proudly and willfully ignorant. They'll literally rather die before changing.