I'd say punctuation characters are those you can use in place of a point.°

So . , ; : ! ? ¿ etc...

Anyway I think this phrasing is lacking perlvar lists some special variables which are not punctuation but global, like $@ or %INC

Update

So that's the definition I found online, wider than I thought but clearly not covering @

Punctuation characters are symbols used in writing to clarify meaning and indicate pauses or stops. The 14 primary punctuation marks in English include the period, comma, question mark, exclamation point, colon, semicolon, dash, hyphen, parentheses, brackets, braces, apostrophe, quotation marks, and ellipsis.

°) "Punkt" is point in German, so it may be more obvious for me, "point" is most probably a French "mutant" of a Latin word like "punctum"