What is the error message that the user encountered in the PHP code?

The error message the user encountered in the PHP code is "Undefined variable". This error occurs when a variable is used without being defined or initialized beforehand. To solve this issue, make sure to define the variable before using it in the code.

// Define the variable before using it
$variable = "Hello World";

// Now the variable can be used without encountering the "Undefined variable" error
echo $variable;