Denatured alcohol is ethanol or grain alcohol that contains additional chemicals called denaturants and makes it unfit for human consumption. It is obtained by adding one or more chemicals (denaturants). Denaturation refers to the removal of properties from alcohol (the possibility of drinking), and not to chemical alteration or decomposition, so that denatured alcohol contains ordinary ethyl alcohol.
Denaturants can be chemicals that cause alcohol to taste bad or simply be toxic.
One of the most common toxic denaturants is methanol or methyl alcohol.