“Agreement: Syntactic relation between words and phrases which are compatible, in a given construction, by virtue of inflections carried by at least one of them. E.g. these and carrots are compatible in the construction of these carrots, because both are inflected as a plural. Likewise, in the Italian sentence Maria e Luisa sono arrivate ‘Mary and Louise have arrived,’ sono (lit. ‘be-3pl’) agrees in respect of plural number with arrivate (‘arrived-FEM.PL’) and both, or sono arrivate as a whole, agree with a subject, Maria e Luisa, which refers to more than one woman.
Also called concord. Distinctions are drawn between grammatical agreement and notional agreement; also between agreement and some similar relations of compatibility, such as the government of cases by prepositions. But this last distinction is often at best imprecise.”
Excerpted from: Matthews, P.H., ed. The Oxford Concise Dictionary of Linguistics. New York: Oxford University Press, 2014.