Simply alcohol refers to ethanol and it's a pretty controversial ingredient. It has many instant benefits: it's a great solvent, penetration enhancer, creates cosmetically elegant, light formulas, great astringent and antimicrobial. No wonder it's popular in toners and oily skin formulas.
The downside is that it can be very drying if it's in the first few ingredients on an ingredient list.
Some experts even think that regular exposure to alcohol damages skin barrier and causes inflammation though it's a debated opinion. If you wanna know more, we wrote a more detailed explanation about what's the deal with alcohol in skincare products at alcohol denat. (it's also alcohol, but with some additives to make sure no one drinks it).