The chemical formula "2 OH" can represent either two hydroxide molecules or two hydroxyl molecules. Both molecules have the same chemical formula, but they differ in their properties.
Hydroxide is a negatively charged molecule, also known as an anion. It offers ionic properties to compounds it is part of due to its negative charge affecting other molecules around it, and it is made of one hydrogen atom and one oxygen atom. Hydroxyl is a common component of organic molecules, especially alcohols. The hydroxyl found within alcohols has little to no charge, resulting in chemical properties that distinguish it from hydroxide. Hydroxyl molecules are a defining feature of all alcohols.