Timelines are referred to as "steered" or "unsteered". Steered timelines are ones where the author seeks to create a specific world or events, and as such the events of the timeline help reach that goal. For example: an unsteered timeline might ask "what if Mark Anthony won at Actium?". A steered timeline might ask "how can I have Roman Republic last longer?" and determine "Mark Anthony wins at Actium". Unsteered timelines are held in higher esteem than steered ones, but a steered timeline can be just as plausible or even more so.
Similarly, there's "hard" and "soft" alternate history. Hard AH focuses on the history itself, and soft AH focuses on the world created by this history (soft AH is always steered). An example would be anything from AH.Com versus Fallout; the latter uses AH only as an explanation of why the world is the way it is.