Working around the front or the back of a post of the previous row gives an interesting raised ridge on the crochet fabric. Around-the-post double crochet is worked by inserting the hook from the
front or back and around the post of the double crochet of the previous
row. While this technique is commonly worked in double crochet, the same methods can apply to single or treble crochet.
For these instructions, we're going to show you how to pick up and work around the back post in double crochet.
Yarn over, insert hook from back to front to back around post of stitch to be worked, yarn
over and pull up loop [yarn over, draw through 2 loops on hook] 2 times.
Here's a video demonstrating how to make post stitches in crochet.
You can also find instructions in Crochet Me's glossary for similar techniques including: