A term used for the central operation within a number of recent grammatical theories, which have been termed ‘unification-based approaches to grammar’. Unification is the merging of two descriptions to form a more specific description which is consistent with both. For example, a noun in description D1 might be specified for countability but not for case, whereas in D2 the same noun might be specified for case but not countability. The two descriptions could then be unified, and any operations which could be carried out on either of the original descriptions could then be performed on the unified description. The approach has advantages for grammatical analysis, in that it allows a grammar to specify constraints on the language without having to state the order in which the constraints are applied: regardless of the number of unifications it takes to fully specify a category, these unifications can be applied in any order. The approach thus has advantages for computational parsing, in that it allows a parser to work with partial descriptions, gradually accumulating information about a grammatical category as it deals with different entries in the lexicon.