What is it?
What do we mean by 'the future'? Whilst this might seem a bit of a non-question, qualifying what we mean is quite essential in any discussion of the future.
Do we mean tomorrow? Do we mean next week? Next year? Or at some imaginably distant future hour? Clearly, our discussion of the future will be very different depending upon how far ahead we are looking... but by 'the future' all we mean is 'that which hasn't yet happened'.
One important thing to note, is that we can remain neutral as to whether the future is predictable or entirely random; whether it is somehow already determined and there is only one potential future, or whether there are many different futures. Therefore our definition of the future does not need to reach as far as 'that which hasn't happened yet, and is not fully predictable' or the alternate view 'that which hasn't happened yet, though if we knew enough about the state of the universe could be fully predicted'.
We can also remain neutral on whether the future includes branching universes for humanity or parallel universes, whereby we may suddenly branch into other universes. These may or may not exist, but we will restrict the scope here to that which we can know about and observe - the observable universe.
Finally, let's remain neutral on the question of whether time is a fourth dimension or is totally separate from the three dimensions of width, height and depth. And also, in most discussions we can remain neutral on the metaphysical nature of time - e.g. whether time 'flows', or what sort of phenomenon it is - something entirely independent or perhaps a fully dependent epiphenomenon of causation (cause and effect).
Therefore our overall scope may become "that which has not yet happened, regardless of whether it can or cannot be fully determined, in the observable universe". It may sound a bit of a long-winded definition, but it is useful to think about. Think on this: If you were writing about the future, would you write in a different way if you thought the future was totally unknown or was fully knowable?