android meaning of @null in xml attribute

I found the following attribute in one xml layout:

android:background="@null"

What is the meaning of @null? What is the difference between specifying background="@null" and omitting background attribute?

If I remember correctly, omitting the background attribute sets a default background. However, explicitly setting background to "@null" removes the background, causing whatever is below the element to be shown. In particular, if you for instance set the background of a Button to null, the border of the button will also be gone (and the button effectively will not really look like a button at all).

What i have observed if i do android:background="@null"or android:background="@android:color/transparent" both have same effect, they just remove the background of the view, so you will see the background colour of the view which is beneath this view.