To me a game is simply an interactive experience with a (self-contained) goal. If it's software on top of that, it's a video game.

I hear the question of whether or not visual novels are games brought up every now and then and as far as I'm concerned they're more or less a subcategory of games but can just as well be considered their own medium. With them being software and having interactive elements most of the time (some even including actual gameplay), they're certainly closer to games than anything else.