1. attempting to visually see future events (crystal balls, scrying, etc.) , or

2. interpreting symbols pertaining to the future (tarot, tea leaves, runes, etc).

It's possible to argue the two are the same.

The thing to remember is that the future is not set in stone. It is a collection of probabilities, some more probable than others. There are certains events in play right now that have likely outcomes, some are very highly probable, some are just possible and some won't happen if the slightest new variable is introduced.

Because of this, divination cannot be an exact science. For example, if you used scrying and picked up an image of something happening late this year that event is what is likely to happen based on how events are right now. It is subject to change depending upon other things that may pop up and intervene, and that depends upon how strong the influences and circumstances are right now that will lead to the seen outcome.

With symbol interpretation (tarot, etc) the reader is seeing the events in play and the events likely to be in play over the time span being viewed. With this type of divination it the reader won't see an exact outcome, but their prediction is likely to be stronger because they are seeing influences present and future, and those are what will shape what happens.

Because of all the variables it is best to use divination techniques for near future events. The further out you look the more likely other probabilities will occur and influence the event in question.