Grafting is the method by which the toe end of a sock is closed off. It involves dividing the last stitches of the sock toe onto two needles and putting the working yarn on a sewing needle.
The stitches are then worked off the needles one by one from front to back in a method that makes the finished edge look like a solid piece of knitting. It takes some practice to get good at grafting but it makes a beautifully finished sock.

