An acid-base reaction is, as the name suggests, a chemical reaction that occurs between an acid and a base. As defined by Johannes Bronsted and Thomas Lowry in 1923, an acid is anything that ‘donates’ a proton and a base is anything that ‘accepts’ a proton.
An acid-base reaction removes a hydrogen ion from an acid and adds it to a base. An acid with a removed hydrogen atom is known as a conjugate base. A base after accepting a proton is known as a conjugate acid. Water is amphoteric, meaning it can act as both a base and an acid.