Meaning of “determiner” - Learner’s Dictionary

determiner

noun [ C ] uk us /dɪˈtɜːmɪnər/

B2 a word that is used before a noun or adjective to show which person or thing you are referring to. For example 'my' in 'my old car' and 'that' in 'that man' are determiners.

(Definition of “determiner” from the Cambridge Learner’s Dictionary © Cambridge University Press)