Door check strap - there's a sprung roller in the mechanism in the door, either the spring's broken or the mechanism has dropped to bits.
Usually, you replace the whole thing, in Honda parts terminology it's listed as a "checker complete", driver's side front door part number is 72340-SAA-J01. They are handed, obviously.
You might be able to find a secondhand one, but the driver's side is most in demand as it's usually the first one to fail.