A Lewis base is a chemical species that can donate an electron pair to form a covalent bond. This definition is part of the broader Lewis theory of acids and bases, which categorizes substances based on their ability to accept or donate electrons. Lewis bases typically include molecules or ions with lone pairs of electrons, such as ammonia or hydroxide ions. In reactions, a Lewis base interacts with a Lewis acid, which is an electron pair acceptor. This interaction leads to the formation of a coordinate covalent bond, where both electrons in the bond come from the Lewis base. Understanding Lewis bases is essential in various fields, including organic chemistry and biochemistry.