Scotch Stitch is one of the three basic block stitches. It consists of at least five stitches creating a square, like this:
You can vary this stitch in so many ways. You can make it bigger:
You can put it into a frame of Continental Stitches, creating Framed Scotch Stitch.
You can divide up some of the longer stitches, to get a stitch which looks like a pillow with a button in the center, called Divided Scotch..
You can change the direction of each block, making Alternating Scotch. This is particularly good if you are stitching a check.
You can offset each row from the ones around it, so the finished result looks less blocky. Offset Scotch makes a great background.
You can share the smallest stitch between to units and make a charming diagonal pattern, Diagonal Scotch.
And if you make those smallest stitches in a different thread, you get a stitch called Hesitation Stitch.
This is just a small sampling of the many Scotch Stitch variations.