Motte and bailey (MAB) is a combination of bait-and-switch and equivocation in which someone switches between a “motte” (an easy-to-defend and often common-sense statement, such as “culture shapes our experiences”) and a “bailey” (a hard-to-defend and more controversial statement, such as “cultural knowledge is just as valid as scientific knowledge”) in order to defend a viewpoint. Someone will argue the easy-to-defend position (motte) temporarily, to ward off critics, while the less-defensible position (bailey) remains the desired belief, yet is never actually defended.
In short: instead of defending a weak position (the “bailey”), the arguer retreats to a strong position (the “motte”), while acting as though the positions are equivalent. When the motte has been accepted (or found impenetrable) by an opponent, the arguer continues to believe (and perhaps promote) the bailey.
Note that the MAB works only if the motte and the bailey are sufficiently similar (at least superficially) that one can switch between them while pretending that they are equivalent.