What is a game?

One of the best and most direct definition of a game is found in The Art of Computer Game Design, written in 1982 by Chris Crawford:

Games are a fundamental part of human existence. The parlance of games has insinuated itself into our language to refer to activities that are not truly games. We play along with activities we find distasteful. We play ball with those who require our cooperation. We play games when we are insincere. A willing participant is game for the enterprise. This broad penetration of gaming concepts into the entire spectrum of human experience presents us with two potential barriers to understanding games.

First, our liberal use of gaming terms promotes an exaggerated perception of our own understanding of games. We fail to render unto the subject the careful and critical analysis that we tender to more academic topics, and we blithely ignore the complexities of game design. Complete amateurs whose only relevant skill is programming undertake to design games with no further preparation than their own experience as game players. Those who overrate their own understanding undercut their own potential for learning.

The second obstacle is ambiguity. We have applied the principles and concepts of gaming so widely that we have watered down their original meanings. There is no longer a clear focus to the concepts we seek to understand. Game designers have no well defined set of common terms with which to communicate with each other. Discussions of game design frequently disintegrate into arguments over semantics. To cut through the tangled undergrowth that has grown up around gaming we shall need the bulldozer and the scalpel.