But there is a difference in meaning between the one- and two-word versions: when you type anyone, you're referring to people; when you type any one you may be referring to people, but not necessarily--it depends on what follows or what is understood. It is used when there are no qualifications to the grouping. The indefinite pronoun "anyone"—used as a single word—refers to any person at all, but not to any particular individual. Anyone or any one: Anyone or any one, both are grammatically singular, regardless of meaning.

Here are a few examples of its use in real sentences: Anyone is an indefinite pronoun that refers to an unspecified person. "Any one"—used as two words—is an adjective phrase that refers to any single member of a group of either people or things.
We use them with a … Anyone, anybody and anything are indefinite pronouns.
Anyone means anybody or any person. Anyone is a synonym of its fellow pronoun anybody. If you need a person to do something, but it doesn’t really matter which person it is, anyone is the word to use. Anyone or any one Anyone is a pronoun that indicates any person. It refers to an individual in a group; which one doesn’t matter. Something could belong to anyone if there are no distinguishing marks or … Anyone is the usual choice in negative statements and in questions: There wasn’t anyone in the lobby. "Any one… We use anyone, anybody and anything to refer to both an open, unlimited set of things or people and specific things or people.