What is time?

It is something completely intangible.

As said, time is an abstraction.

Time is the most intangible, most abstract concept possible.
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And, actually, there is no real definition for time, right?

We measure time by things we do, by things that happen between some abstract point A and abstract point B.

The matter is that, actually, we have to make agreements, social agreements, because we have to fix when we meet, when we do what. Because, I am full of appointments.