A determiner is used to modify a noun. It indicates reference to something specific or something of a particular type. This function is usually performed by articles, demonstratives, possessive determiners, or quantifiers.
Determiners include the following common types:
Articles: a/an, the
Demonstratives: this, that, these, those
Possessives: my, your, his, her, its, our, their, xs (possessives)
Quantifiers: (a) few, fewer, (a) little, many, much, more, most, some, any, etc.
Numbers: one, two, three, etc.