A half double crochet is a basic stitch pattern. It is a common stitch pattern and offers a tight sheet when combined into multiple rows.
Crochet is the process of using a needle to create a piece of cloth. There are a number of crochet patterns but beginners tend to start with the single crochet, which is basically a chain of loops, or stitches.
A half double crochet requires a single crochet chain, which is called the foundation chain. The process of creating a half double crochet involves pulling three loops onto the hook to create one stitch. The process is repeated down the length of the foundation chain and then in additional rows until the fabric is to the desired length.