A determiner is a word or a group of words that specifies, identifies, or quantifies the noun or a noun phrase that follows it. It is also known as a prenominal modifier.
Determiners include articles (a, an, the), cardinal numbers (one, two, three…) and ordinal numbers (first, second, third…), demonstratives (this, that, these, those), partitives (some of, piece of, and others), quantifiers (most, all, and others), difference words (other, another), and possessive determiners (my, your, his, her, its, our, their).