This document defines acids and bases and discusses their uses. Acids are compounds that donate protons and yield hydronium ions in water, and can be used to remove rust and in food production. Bases are compounds that accept protons, and can be used as catalysts and to neutralize acids. The document also notes there are nine definitions for acid-base reactions, including the Lavoisier, Arrhenius, and Brønsted-Lowry definitions.