Heel Flap

From KnitWiki

A type of heel for hand knit socks.

This heel is formed by working only the back stitches of the sock for a couple of inches. Usually the flap is worked with slipped stitches alternating with knit or purl stitches to create a thicker, more durable fabric to rub up against the back of the shoe. When the flap is knit to the desired length, a small amount of shaping is done to form a cup for the heel, usually using short rows. Then stitches are picked up on the sides of the flap to work the foot.

Other types of heels are possible without using a heel flap