Glycerin, or glycerol, is a sugar alcohol generally found in the form of a transparent, odorless liquid. Its main uses are as a solvent or a reduced-calorie sweetener. It has a boiling point of 290 degrees Celsius, significantly higher than water, which boils at 100 degrees Celsius.
Glycerol is a diuretic and laxative, meaning regular intake of it can contribute to dehydration. That being said, the general consensus is that glycerol is safe for human consumption. In fact, most people have used glycerol in various household products including food, shaving cream, soaps, and hair products. Glycerol is also useful as an anti-freeze, although it's been replaced with ethylene glycol.