Stockinette stitch is the most common knitting fabric, made by alternating a knit row with a purl row. It produces a smooth surface of V-shaped stitches on the front and bumpy purls on the back, and naturally curls at the edges.
Because stockinette curls, garments usually pair it with a non-curling border like ribbing or garter stitch. Its smooth face is the classic backdrop for colorwork and the reverse (the bumpy side) is called reverse stockinette.