Text mode demo
A demo that may only draw with characters — a grid of perhaps 80×50 cells in 16 colours — and still has to look like real-time graphics.
The constraint is the point. A text mode demo typically renders 3D, plasma and particles into an internal framebuffer, then maps each cell to the character and colour pair that comes closest, using the half-blocks and shade characters of code page 437 as a brush. Libraries such as AA-lib and libcaca do the same job generically, but demo groups tend to write their own converters to wring extra sharpness out of the grid.
The form has its own recurring competition, TMDC (Text Mode Demo Contest), held online, and also appears as a separate compo at demoparties. It sits somewhere between ANSI art and conventional demo coding, and draws people from both camps.