\thinspace & \negthinspace ¶Synopsis, one of:
\thinspace \negthinspace
These produce unbreakable and unstretchable spaces of 1/6em and
-1/6em, respectively. These are the text mode equivalents of
\, and \! (see Spacing in math mode/\thinspace).
You can use \, as a synonym for \thinspace in text mode.
One common use of \thinspace is as the space between nested
quotes:
Killick replied, ``I heard the Captain say, `Ahoy there.'\thinspace''
Another use is that some style guides call for a \thinspace
between an ellipsis and a sentence ending period (other style guides,
think the three dots and/or four dots are plenty). Another
style-specific use is between initials, as in D.\thinspace E.\
Knuth.
LaTeX provides a variety of similar spacing commands for math mode
(see Spacing in math mode). With the amsmath package, or as
of the 2020-10-01 LaTeX release, they can be used in text mode as
well as math mode, including \! for \negthinspace; but
otherwise, they are available only in math mode.