The most basic knitting stitches are stocking stitch, visible in the upper right corner of this picture. In the U.S., we call it stockinette, but it is the stitch used to make stockings, back when people knitted stockings.
Stockinette is made by knitting all the stitched on the right side and purling all the stitches on the wrong side.
The tops of stockings were done in garter stitch: knitting all the stitches. The green in the picture above is garter stitch in a small gauge. It’s like a mass of pearls.
The gray has a band of garter stitch in a larger gauge. It shows “reggies” — ridges of purl stitches.
Garter stitch stays flat. Stockinette rolls. That’s the biggest difference.
Now you know.