OH⁻ is hydroxide ion, which acts as a strong base by accepting protons (H+) during chemical reactions.
A base is a substance that can accept protons (H+) in a chemical reaction.
The conjugate base of an acid is formed when the acid loses a proton. In this case, OH⁻ would be considered the conjugate base if it gains an H+ from another species.
An acid is a substance that can donate protons (H+) in a chemical reaction.