The Brønsted-Lowry theory is a fundamental concept in chemistry that defines acids and bases based on their ability to donate or accept protons (H⁺ ions). According to this theory, an acid is any substance that can donate a proton, while a base is any substance that can accept a proton. This definition broadens the understanding of acid-base reactions beyond just the presence of hydroxide ions. This theory is widely used to explain various chemical reactions, including those in aqueous solutions. It helps in predicting the behavior of substances in reactions, making it easier to understand processes in fields like biochemistry and environmental science.