If you use ordinary wood stain on a deck you will quickly find out the difference. Deck stain is designed to be used outdoors and be walked on, without the need for a protective clear coat. Ordinary wood stain has no UV inhibitors, low grade resins and must be protected with a clear finish (varnish, etc).

Deck stains can last for a year or more on a properly prepared wood deck. Ordinary wood stain might last a month if your lucky.