Einstein once wrote something like the following about time, which I think is very succinct and pretty much describes it.
When an individual ponders his experiences, he can order the events in his life using the criteria of before and after. He can assign a number to each event in such a way that events assigned a lower number occurred before events assigned a higher number.
It is convenient to use a device called a clock to provide a consistent set of numbers for use in ordering events.
In describing the laws of physics using the language of mathematics, it is convenient (if not necessary) to use a continuous variable called time. This variable similarly orders events based on the criteria of before and after.
There is little (if anything) more that can be said relating to time.
he above is not a quote: It is a paraphrase based on my not infallible memory. I Think it is from the preface to one of his books or essays on Relativity. I have read several articles containing very lengthy & confusing verbiage which did not seem to describe the concept of time any better than the above.
It is interesting that Albert used bold or italics for
before & after, implying that they should be considered primitive terms, not definable via the use of simpler terms or concepts.
Note that an axiomatic system requires undefined primitive terms to avoid various problems associated with circular definitions.
It is interesting that Albert did not mention the concept of the flow of time from past through the present into the future, which does seem to be a construct (illusion?) of the human mind rather than an objective process associated with reality.