A Possible Future is a resultant future that occurs from a given time-line that diverged at a single point in time. in comics, this point is usually considered the present day, and the possible future is a speculative occurrence that may or may not happen in the official continuity. The possible future usually focuses upon a single event, or in cases of comics, around a single character or organisation. The Possible Future can be shown in order to give clues about a current storyline, or can be used for dramatic effect, used for stories that are set in the future (such as the Legion of Superheroes), for fan-service, or used simply to make a comic series in and of itself. They may occur so that comic creators can create suspension, or can be created via time traveling within the comic, or a similar event.
The Possible Future, as its name suggests, is a future result that may or may not happen, and is in flux so that a different resultant future may possibly occur. The 31st century look at the Green lantern Corps., when Sodam Yat is the last Green Lantern and Last Guardian of the Universe, is thought (and hoped) to be a Possible Future, instead of the established one