so like, Math. round (2.2) ,,, so 2.2 is the property here ?

As shown, 2.2 is the argument being passed to the Math.round function.

Math is the object while round is the property of the object. So round is a property of Math. Round is also a function that takes a value in its parameter, that value is referred to as an argument. Functions can be properties of Objects just like any regular Object property. For example in an object literal:

 let users = {username:"Steve", pass:"5001", email:"stev01@gmail.com", function() {return this.username + this.email;}};

The object here is users and its properties are username, pass, and email, but it also has a property which is a function that returns username + email.

To access these properties you could use the dot notation or bracket notation. For example:

let currentUser = users.username;

Hopefully this answers any future questions and sorry for the late post! Happy Thanksgiving by the way :D