If I saw your message, I would think "what is a 'simple name'?".  There's no glossary entry for that, nor is it a concept used elsewhere in the documentation as far as I remember.  One could instead use "single identifier",  but the problem with both of those is that "end" *is* a simple name/single identifier.  The error isn't that an identifier was not used, the error is that an expression was used.  We unfortunately can't read the mind of the programmer to know that the *actual* error was using a '+' instead of a ','.