A period during which something, whether action, process or condition, exists or continues; an interval comprising a limited or continuous action, condition or state of being. In order to describe any action or motion one must note the ‘time’ as well as the ‘space’ involved. Nobody really knows what time it is or even if it has an objective existence, any more than one really knows what space, motion, matter or energy are. All are defined in relation to one another and ultimately in terms of human perception. All are relative.