What is a casual video game

A "casual game" is a game that can be played by anyone, the gameplay simple to grasp, but it is called casual because people who play games such as CoD:MW, HALO 3 and other action-y games find these games slow paced and boring, thus they christened them "casual games."

a few examples are:

mario party 1-8
wii fit/plus
nintendogs
Animal crossing wild world

any sort of game that anyone can play easily and very rarely that hard to complete.