what is typedef in dart code example

Example 1: dart typedef

typedef ManyOperation(int firstNo, int secondNo);   // function signature to match
Subtract(int firstNo, int second){
   print("Subtract result is ${firstNo-second}"); 
}  
Calculator(int a, int b, ManyOperation oper){ 		// matches function signature
   oper(a,b); 
}  
main(){ 
   Calculator(5, 5, Subtract); 						// 'Subtract result is 0'
}

Example 2: dart typedef

//Return type not part of typedef

typedef function_name(parameters)