A base is a substance that has the ability to accept protons (H+) during a chemical reaction.
An acid is a substance that can donate protons (H+) in a chemical reaction.
The conjugate base of an acid is formed when the acid loses its proton. It represents what remains of the acid after donating H+.
Hydroxide ion (OH⁻): OH⁻ acts as one of the most common examples of bases, being able to readily accept H+ ions.