Alcohol, the liquor people consume has very many industrial and other uses. It is used in laboratories and clinics as fuel in the spirit lamp. It is also used in the stoves in camps and parties. Apart from this, alcohol-chemically called Ethyl alcohol- is a universal solvent and is needed for many industries and medicine manufacturing and hospitals for sterilising and cleaning.
So there is possibility of this being misused for drinking.
Hence to prevent people from misusing and consuming as liquor, the spirit or ethyl alcohol used for such purposes is mixed with some other chemicals, mostly methyl alcohol. The added substance make the spirit emanate offensive smell, prohibiting taste and is toxic and cause vomiting etc.
The alcohol or spirit thus mixed with methyl alcohol ,or other chemicals is called Denatured alcohol or Denatured spirit. If methanol is added then it is also called methylated spirit.
The denatured spirit is handled under proper control and inventory measures I the user and supplier ends. But even then sometimes we get to read reports of people selling or consuming spurious liquor, which is usually the methylated spirit. Consumption of methylated denatured spirit will lead to victims to bad consequences; it can cause blindness.