Identifiers are used to define variables, functions or other user-defined variables. Identifiers start with a letter, a dollar or an underscore. They cannot start with a number. Here are some examples of valid identifiers −

def employeename 
def student1 
def student_name

where def is a keyword used in Groovy to define an identifier.

Here is a code example of how an identifier can be used in our Hello World program.

class Example {
   static void main(String[] args) {
      // One can see the use of a semi-colon after each statement
      def x = 5;
      println('Hello World'); 
   }
}

In the above example, the variable x is used as an identifier.