Definiteness refers to a grammatical component of nominals that denotes specificity of identification or ambiguity. This specificity can be marked by articles or by affixes. Example: Definite: “the glass of water†Indefinite: “a glass of water
A grammatical feature belonging to DPs ( the/this/that, etc.) that mark specificity. Definiteness can influence the agreement spell-out of a verb: e.g., [-Def A number] of students * is/are vs. [+Def The numbe of students is/*are.
In grammatical theory, definiteness is a feature of noun phrases, distinguishing between entities which are specific and identifiable in a given context (definite noun phrases) and entities which are not (indefinite noun phrases).