a (algebra|of a lattice) in which every set with a lower bound has a greatest lower bound.
a (math|of a category) In which all small limits exist.
a (logic|of a proof system of a formal system) with respect to a given semantics, that any well-formed formula which is (semantically) valid must also be provable.Sainsbury, Mark [2001] Logical Forms : An Introduction to Philosophical Logic. Blackwell Publishing, Hong Kong (2010), p. 358.