What does the word purl mean in knitting?

Purl is a knitting stitch, which can be paired with normal stitch to make ribbing, stockinette stitch and a few others. Purling is very simple, it is a bit like normal knitting in reverse.

To purl, you insert the right needle into the stitch from top to bottom, right to left, the right needle should go in front of the left. You should now be holding the needle in an X shape with the right needle in front of the left needle and the working yarn in front of both needles. Then you wrap the yarn around in between the needles and back around the front needle. Slip the front needle around to the back and lift the new stitch up and off the left needle. You should now have one new stitch on the right needle.