related to Linux `fbdev` abstraction (a.k.a. Linux framebuffer), as well as to accessing the framebuffer (a part of video memory) in general
Framebuffer is a part of video memory where (current) video frame is stored, pixel by pixel.
In Linux kernel, fbdev is a graphic abstraction layer for accessing that memory. Different video hardware needs different drivers, that may be loaded as kernel modules, but user-space software uses unified API writing to it. See http://tldp.org/HOWTO/Framebuffer-HOWTO/ for details.
