decrease (dec)

To do a decrease stitch. The hook inserts the next stitch, do a yarn over and brings yarn through the stitch we just insert.
  At this time, we continue to insert the next stitch and then do a yarn over, then through the stitch we just insert.
  Now we have 3 loops on the hook, do a yarn over, and bring yarn through all 3 loops. An increase stitch finish.
  Do it again…… It's called decrease.

Video

①

The hook inserts into the next stitch.

②

Do a yarn over and brings yarn through the stitch hole we just insert.

③

Continue to insert the hook into the next stitch and then do a yarn over and bring the yarn through the stitch we just insert.

④

Now we have 3 loops on the hook.

⑤

Do a yarn over, and bring yarn through all 3 loops.

⑥

There 1 loop left on the hook. An decrease stitch finish.