As far as I am able to tell from my reading, science still does not have a commonly agreed definitive definition of time but Julian Barbour's is the description that resonates most with me (ref. Wikipedia)
In 5th century BC Greece, Antiphon the Sophist, in a fragment preserved from his chief work On Truth, held that: "Time is not a reality (hypostasis), but a concept (noêma) or a measure (metron)." Parmenides went further, maintaining that time, motion, and change were illusions, leading to the paradoxes of his follower Zeno. Time as an illusion is also a common theme in Buddhist thought.
J. M. E. McTaggart's 1908 The Unreality of Time argues that, since every event has the characteristic of being both present and not present (i.e., future or past), that time is a self-contradictory idea (see also The flow of time).
These arguments often center around what it means for something to be unreal. Modern physicists generally believe that time is as real as space—though others, such as
Julian Barbour in his book The End of Time, argues that quantum equations of the universe take their true form when expressed in the timeless realm containing every possible now or momentary configuration of the universe, called 'platonia' by Barbour. (See also: Eternalism (philosophy of time)