Determiners are words which quantify or identify nouns. In English, determiners include articles, quantifiers, demonstratives, and possessive pronouns. They typically precede nouns and offer grammatical information about them (e.g. whether or not the nouns are indefinite or definite).
In languages that are more synthetic than English, determiners may be prefixed or suffixed to the noun, or even change the noun's form. e.g. Swedish bok (book), when definite, becomes boken (the book).
The following classifications are specific to English, and may not have equivalents in other languages. For example, articles (and definiteness) have no equivalent in Japanese or Czech.
Articles
Quantifiers
Demonstratives
Possessive pronouns