Ampholytes are substances that can exhibit both acidic and basic properties. They can donate or accept protons depending on the pH of the solution they are in. When an ampholyte is placed in a solution with a pH below its isoelectric point, it acts as an acid and donates a proton. When placed in a solution with a pH above its isoelectric point, it acts as a base and accepts a proton.

Common examples of ampholytes include amino acids, proteins, and certain metal oxides.