A Brønsted acid is a substance that can donate a proton (H⁺) to another substance in a chemical reaction. This concept is part of the Brønsted-Lowry theory of acids and bases, which defines acids as proton donors and bases as proton acceptors. Common examples of Brønsted acids include hydrochloric acid (HCl) and sulfuric acid (H₂SO₄). When a Brønsted acid donates a proton, it transforms into its conjugate base, which is the species that remains after the proton is lost. This relationship is important in understanding acid-base reactions, as it helps predict the behavior of substances in various chemical environments.