Scotch Stitch is one of the three basic block stitches. It consists of at least five stitches creating a square, like this:
Scotch Stitch, diagram copyright Napa Needlepoint
You can vary this stitch in so many ways. You can make it bigger:
Scotch Stitch over 4 threads, diagram copyright Napa Needlepoint
You can put it into a frame of Continental Stitches, creating Framed Scotch Stitch.
Framed Scotch, diagram copyright Napa Needlepoint
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..
Divided Scotch, diagran copyright Napa Needlepoint
You can change the direction of each block, making Alternating Scotch. This is particularly good if you are stitching a check.
Alternating Scotch, diagram copyright napa Needlepoint
You can offset each row from the ones around it, so the finished result looks less blocky. Offset Scotch makes a great background.
Offset Scotch, diagram copyright Napa Needlepoint
You can share the smallest stitch between to units and make a charming diagonal pattern, Diagonal Scotch.
Diagonal Scotch, diagram copyright Napa Needlepoint
And if you make those smallest stitches in a different thread, you get a stitch called Hesitation Stitch.
Hestitation Stitch, diagram copyright Napa Needlepoint
This is just a small sampling of the many Scotch Stitch variations.