( iOS ) What is superview and what is subviews

A superview is a view that holds other views over it and subviews are the views being held/added over a View.

Let's assume we have a view named MyView, which holds a UIButton (named loginButton) over it. Here MyView is considered a superview for loginButton and loginButton is considered a subview of MyView.

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As per the provided code snippet.

[self.view addSubview:self.frontView];

Hence view (Controller's view) is a superview and frontView is a subview

"superview" means the view which holds the current one. "subviews" means the views which are holding by the curent view.

For example, you have a view (will call it as MyView) which include a button. Button is a view too (UIButton is a kind of view). So, MyView is superview for the button. Button is a subview for MyView.