To Hand Wave something is to gloss over or not sweat the details. In terms of story, it's an explanation or story element that's murky, vague, or inconsistently applied. It's the invocation of Willing Suspension of Disbelief via a quick and dubious explanation.
Game and Story Use
- Best advice: Know Your Players (but I say that a lot). If the group is just trying to blow off steam and have some fun, chances are no one will mind a hand wave, especially in regards to Monster of the Week or other challenge that's just here for scene or session. If the game is full of method actors and puzzle solvers, however, then you might need to have a more detailed explanation to keep things from coming apart at the seams.
- The style of game is also a big factor. A Hand Wave goes further in a four-color action-fest or hack and slash dungeon romp than in an investigative plotline. Some campaign styles encourage the players to just roll with it, other styles encourage them to pick at every detail for clues.
- Extrapolating from that, the type of players you have, and the genre of game you're running, might together suggest the level of detail you need in your plots and your mechanics.