http://en.wikipedia.org/wiki/Tuple
It's just a fancy buzzword mostly.
"In mathematics, a tuple is a finite sequence of objects. (An infinite sequence is a family.) Tuples are used by mathematicians to describe mathematical objects that consist of certain components. For example, a directed graph is defined as a tuple (V, E) where V is the set of nodes and E is a subset of V × V that denotes the edges."
In our case the tuple consists of (A, B) where A is a location in the array being switched with B (which is a location in the array.