ISO Latin 1 contains only two space characters:
normal space and
no-break space.
In Unicode, there are other
space characters too, such as
em space (U+2003), many of which are
defined to have some specific width.
The other characters are those in the range U+2000
to U+200B (in the
General
Punctuation block),
ideographic space (U+3000), and
zero width no-break space (U+FEFF). For a brief summary, see
the document
Unicode spaces.
Quite often the phrase whitespace (characters) is used to denote a set of characters or codes which are treated as "empty space". The exact definition varies but typically covers some control codes such as horizontal tab and linefeed, too. See e.g. the definition of "whitespace" in the HTML 4.0 Specification.