GSE or grapefruit seed extract somes from grapefruit seeds. It is usually sold in a liquid form mixed with glycerine. It has many known benefits, but formost among those is it's use as an antibacteria agent. 5-6 drops of GSE in a gallon of water makes ideal feeding water for corn snakes. If corn snakes have persistent regurge problems, 2-3 drops of GSE in a water bowl can sometimes help stop this.
Grape seed extract comes from grape seeds. It is usually found in capsules and has many reported health benefits for humans. I don't know of anyone using it for reptiles.
Mark