When I read books in English, I see sometimes there is a space between "any" and "one" and sometimes there is not any space. So, what is the difference between "anyone" and "any one"?
anyone refers to a single person. If
any one is used by itself, it means the same as
anyone, but it is preferred for it to be spelled without the space. If
any one is used with something else (e.g.
any one of them) it can mean something completely different.
In summary, almost all the time you should use
any one is also an acceptable spelling.
The Oxford English Dictionary (OED) states regarding any one:
"The two-word form any one is not the same as the one-word form anyone and the two forms cannot be used interchangeably. Any one means ‘any single (person or thing)’, as in: not more than twelve new members are admitted in any one year."
Meanwhile, the one word form anyone is defined as follows:
Line breaks: any¦one Pronunciation: /ˈɛnɪwʌn/
Definition of anyone in English: pronoun
1 [USUALLY WITH NEGATIVE OR IN QUESTIONS] Any person or people: there wasn’t anyone there does anyone remember him? I was afraid to tell anyone
1.1 [WITHOUT NEGATIVE] Used for emphasis: anyone could do it
2 A person of importance or authority: they are read by anyone who’s anyone