Glycerol, alternatively spelled glycerin, or glycerine, is a simple sugar alcohol sometimes used as a solvent. It is a polyol, consisting of a propane molecule with one hydrogen on each of the carbons being substituted by a hydroxyl group. Glycerol is sometimes used as a laboratory solvent, though this is made difficult by its high viscosity. It is also used in the manufacture of the well-known explosive nitroglycerin.
Glycerol has several niche uses in home chemistry. A mixture of glycerol and oxalic acid can be distilled to produce formic acid. It can be used as an inert solvent for producing extracts from plants or carrying out organic reactions. And perhaps most famously, it can be nitrated using sulfuric and nitric acids in an ice bath to produce nitroglycerin, a sensitive liquid high explosive used to make dynamite.
Glycerol is a colorless, viscous, and odorless liquid at room temperature with a mild sweet taste similar to artifical sweeteners. It is soluble in water, but has limited solubility in most organic solvents such as acetone, chloroform, and diethyl ether.
Glycerol can be found in many pharmacies and grocery stores where it is used as "skin protectant". As with many medical and health products, it is sold at a very high markup, which means that buying glycerol online from certain wholesalers is actually much cheaper.
Glycerol is produced by the hydrolysis, or saponification, of plant and animal fats using a strong base. It is usually simpler to purchase it rather than go through the process of purifying the product from this reaction, though.
Glycerol is more-or-less nontoxic, as it is an important biological chemical. Food-grade glycerol can be tasted for those that are curious, though external medicinal grades cannot be guaranteed safe for consumption (Sciencemadness user Ave369 used medical grade glycerol to soften homemade vodka, and nothing bad happened to her).
Glycerol should be stored in sealed bottles, as it is hygroscopic and it is extremely difficult to remove the water.
Glycerol poses little toxicity to the environment and can be safely poured down the drain.