E2003 Undeclared identifier '%s' (Object Pascal)
The compiler could not find the given identifier - most likely it has been misspelled either at the point of declaration or the point of use. It might be from another unit that has not mentioned a uses clause.
program Produce; var Counter: Integer; begin Count := 0; Inc(Count); Writeln(Count); end.
In the example, the variable has been declared as "Counter", but used as "Count". The solution is to either change the declaration or the places where the variable is used.
program Solve; var Count: Integer; begin Count := 0; Inc(Count); Writeln(Count); end.
In the example we have chosen to change the declaration - that was less work.