hdc = half double crochet
With 1 loop on hook, wrap the working yarn 1 time; you’ll have 2 loops on your hook. Next insert hook into stitch (can be desired stitch or foundation chain) and wrap working yarn on hook and pull through. You will have 3 loops on your hook. Wrap 1 last time and pull through all 3 of the loops.
Watch Mikey demonstrate for us in the link and video below.