Do not confuse this tag as a "catch-all" tag for all dresses that simply leave the shoulders bare.
If the dress has a low and wide-cut neckline and has attached sleeves that sit on the arms instead of on the shoulders, it is an off-shoulder dress.
If the dress has no attached sleeves and has no support of the shoulders (ie. halternecks, shoulder straps, etc.) to keep it in place, it is a strapless dress.