An ***x/y transition*** is kind of [[paragraph transition]] in which your [[topic sentence]] follows an x/y pattern.
In other words, the first half of the sentence (the "***x***") uses a [[keyword]] or idea from the *previous* paragraph, and the second half of the sentence (the "***y***") links it to or introduces the main idea in this paragraph.
The term is [[The Elements of Academic Style (2014)|from Eric Hayot]]. Here are two examples he gives:
> Despite the successes of the early 1980s [x], Alphaville never managed to break out of its mainly European reputation [y].
>
> Because the novel never resolves this question [x], readers must answer it for themselves [y].
>
> \- Elements, p. 110
Hayot distinguishes between x/y transitions and what he calls "lexical transitions" (i.e., using a keyword from a previous paragraph), but I find these are either very similar in practice to x/y transitions, or there's a sense in which, when he's discussing "lexical transitions," he's not really talking about transitions per say—he's talking about [[keyword|keywords]], as a tool you can *use* for a transition. But they're more widely applicable than that in terms of signalling one's structure. (Indeed, on page 112 Hayot has a really good discussion of using cognates instead of exact keywords that is very relevant to [[subtle signals and metalanguage|subtle signals]].)