What is property in hasOwnProperty in JavaScript

Question

Consider:

if (someVar.hasOwnProperty('someProperty') ) {
 // Do something();
} else {
 // Do somethingElse();
}

What is the correct application/explanation of hasOwnProperty('someProperty')?

Why can't we just use someVar.someProperty to see if an object someVar has a property called someProperty?

In this context, what is property?

What property is checked by this JavaScript?