For purposes of this page I give it my personal definition.
Example: The default leg of a chair (output) may be a long rectangular square. If its maker tapers the ends for no other reason than personal aesthetic preference, that tapering is art. If he tapers it for a functional (mechanical) reason it is part of 'engineering design' and not art. If he makes the leg round as on a lathe it may or may not be an artistic decision.
There are two main aspects of art which cause the most debate.