Motte-and-Bailey speaks to equivocating about positions in argument. There are many other ways to equivocate, e.g. over the meaning of a single word, used in multiple ways in the same argument, as opposed to a retreat to an easier-to-defend position over the initial one presented/being discussed - as in the thread above.

The relationship between the two words is akin to the one between “rectangle” and “square”.