Technical term in grammar and logic for a word or particle that links subject and predicate, such as だ, です, or である in Japanese.
Japanese 'da' and 'desu' are types of copula.
In logic, the copula serves to link the subject and predicate.
Compound of 繋 (connect) and 辞 (word/expression), literally 'connecting word'. The exact historical derivation is uncertain, but the term is a calque from Western grammatical terminology.