It is an imprecise colloquial term used to describe any one of a number of volatile and/or flammable liquids.......
.......most notably "pet spirit" (petroleum spirit, which is a mixture of aliphatic alkanes that has a boiling point in the 35 - 60 degrees celcius range), "white spirit" (a mixture aliphatic and alicyclic C7 - C12 hydrocarbons), and "methylated spirit" (which is denatured ethanol - ethanol with added denaturant, usually methanol or IPA, which renders it undrinkable).
Methyl alcohol is methanol. Methanol is not commonly referred to as "spirit" in my experience.
The term "spirit" usually refers to ethanol.
The alchemists believed they could obtain the essence or spirit of a substance by heating it strongly and condensing the evolved vapours (i.e. distillation).
The term was first applied to spirit of wine, which we now know is 95 % (190 proof) ethanol.
Ethanol is often called grain spirit, because it is often obtained by distilling the fermentation products of various grains.
The term "spirits" now refers to distilled alcoholic beverages in general.
Methylated spirit is not methanol.
It is ethanol that has been made undrinkable by the addition of methanol which is poisonous.
Methanol is often called wood spirit, because it was first obtained by the destructive distillation (pyrolysis) of wood.
A less common meaning of "spirit" is any volatile liquid that is obtained by distillation or cracking.
An example is petroleum spirit (often called petroleum ether), a mixture of hydrocarbons with boiling point 40 °C to 60 °C.