A short definition of a game is: An apparently dynamic system that a player believes is winnable.
A longer one is: A game is a simplified, fair, fascinating, empowering, believable and enclosed world whose purpose is to provide structured play through moderated yet unscripted actions and learnable dynamics, with the goal of winning through victory or achievement.
All games are bounded by six creative constants (fun, lensing, physicality, time, self and profit) and composed of two layers: an abstract mechanistic layer called the frame and aesthetic creative layer called the fantasy. There are many sub-categories of game, such as sports, card games, gambling, pen and paper roleplaying games and videogames.
Games are played and enjoyed for many reasons. For some they are simple distractions or prize-winning opportunities, whereas for others they are lifelong careers. In modern times especially games have often shown themselves to be able to be artistic, to inspire a numinous sense within a player, and a sense of magic. Games are the world's thaumatic art form.
Games are not the only form of play but they do tend to be the most successful in gaining long-term traction. However 'game' as a term is also often misappropriated to include other kinds of interactive entertainment and play primarily as a legitimising or marketing ploy.