Position dancing is a debate technique where a debater never explicitly takes a specific position and is therefore not required to defend it. The freedom to change position as needed also frees the attacker from the need to maintain internal consistency, and leaves them the option to pretend they supported a given position all along if it suits their needs in the moment.
This technique tilts the playing field heavily in favor of the attacker because there are no flawless positions.
Position dancing is a rhetorical deception; it can be seen as a form of topic shifting, where the subject under debate is never clearly stated. It often includes a covert straw man attack, where the attacker subtly shifts the (implied) topic in ways which leave the defender apparently defending views whose defense is not necessary in order to defend the original point (and which may even be views the defender does not hold).
This technique is most commonly used in support of conservative viewpoints, as it tends to favor the status quo by allowing easy demolition of new ideas without exposing pre-existing beliefs to equal scrutiny.
In general, position dancing can be fought by encouraging debaters on a given issue to make position statements addressing the particular issue in question. It may be helpful (especially if it seems to be difficult to get the debater to be specific or thorough) to develop a position quiz on the issue in question (if one does not already exist) and ask the debater to respond to it.