Denatured alcohol is ethanol with added adulterants that make it useless for consumption as an intoxicating beverage by rendering it toxic or extremely distasteful to drink, but still useful for industrial processes or as a household chemical. This is done in order to make it exempt from taxes that apply to potable alcohol. 

Ethanol, also known as ethyl alcohol or grain alcohol, is a flammable, colorless chemical compound, one of the alcohols that is most often found in alcoholic beverages. In common parlance, it is often referred to simply as alcohol. Its molecular formula is C2H6O, variously represented as EtOH, C2H5OH or as its empirical formula C2H6O. 
Isopropyl alcohol or isopropanol is a common name for propan-2-ol, a colorless, flammable chemical compound with a strong odor. It has the chemical formula CH3CHOHCH3, and is the simplest example of a secondary alcohol, where the alcohol carbon is attached to two other carbons. It is an isomer of propan-1-ol.
(answer from wanker_fantass)