Tommy at All Things FPL:
A rotation pair is two clubs whose fixtures when combined provide a sustainable fixture route as the gameweeks progress. Often these can be found as home rotation pairs where two clubs alternate their home fixtures to provide a fantasy manager with a position in their starting XI that is always at home. Used predominantly in defence, rotation pairs can be seen as the cornerstone of any squad as these pairs barring injury can be left alone allowing fantasy managers to prioritise their transfers on more important matters such as transferring in the surprise package, big hitters with the upcoming fixtures or players who have displayed incredible previous form.
Disclaimer: I write for All Things FPL.