For compiled languages, syntax errors are detected at compile-time.
In 8-bit home computers that used BASIC interpreter as their primary user interface, the SYNTAX ERROR error message became somewhat notorious, as this was the response to any command or user input the interpreter could not parse.
A syntax error can occur or take place, when an invalid equation is being typed on a calculator.
This can be caused, for instance, by opening brackets without closing them, or less commonly, entering several decimal points in one number.
A compiler will flag a syntax error when given source code that does not meet the requirements of the language's grammar.