The Unicode character U+2009 represents the "Thin Space", a whitespace character designed to create a space narrower than a standard space (U+0020) but wider than some other space characters like the Punctuation Space or Figure Space.
You can copy Thin Space here and use it wherever you like:
| Unicode | U+2009 |
|---|---|
| HTML Entity |   or   |
| LateX | \thinspace |
| CSS | \u2009 |