what does map do in flutter code example

Example 1: Map in dart

void main() { 
   var details = new Map(); 
   details['Usrname'] = 'admin'; 
   details['Password'] = 'admin@123'; 
   print(details); 
} 

// Output
// {Usrname: admin, Password: admin@123}

Example 2: what is map in dart

void main() { 
   var details = new Map(); 
   details['Username'] = 'admin'; 
   details['Password'] = 'admin@123'; 
   print(details); 
}