An existential determiner is a word used to indicate the existence of something, typically introducing a noun phrase that presents new information. In English, the most common existential determiner is "there," often used in constructions like "There is a book on the table" or "There are many options available." These phrases suggest that something exists without specifying a particular noun beforehand. Existential determiners help to introduce or highlight the presence of something in a conversation, allowing speakers to present new ideas or items in a clear and direct manner.