MAME "VideoSnaps" are short movies meant to be used by MAME Frontends and menu systems, playing a short example of the game's title screen, gameplay, and other notable visual cues. They are not required for MAME to play the games.
MAME (an acronym of Multiple Arcade Machine Emulator) is a free and open source emulator designed to recreate the hardware of arcade game systems in software on modern personal computers and other platforms. The intention is to preserve gaming history by preventing vintage games from being lost or forgotten. The aim of MAME is to be a reference to the inner workings of the emulated arcade machines; the ability to actually play the games is considered "a nice side effect". Joystiq has listed MAME as an application that every gamer should have.