Methanol

From Webster:

A light volatile flammable poisonous liquid alcohol CH₃OH used especially as a solvent, antifreeze, or denaturant for ethyl alcohol and in the synthesis of other chemicals.

It is made during the degradation of pectine so it is an ingredient of most fruit wines. By distilling these wines it is concentrated in the distillate.

There is widespread belief it can be removed by throwing away the fores and heads, but that is a false belief, as it is also present in the tails.

On the other hand: the belief that a lot of deaths by drinking poisonous alcohol are caused by methanol due to bad fermenting or distillation, is a false belief too. In most of these cases the poison was deliberately added after distillation.