‘Petranese’ refers to the Black Sheep Crochet specific way of describing the correct placement of overlay crochet stitches.
Tutorials for some of the special stitches, how to count rounds and other techniques commonly used in Black Sheep Crochet designs can be found here:
https://blacksheepcrochet.com/petranese-explained-describing-overlay-crochet-stitch-placement/
They complement the “How to…” tutorials mentioned above.