Would someone please explain to me what the below paragraph means? This is a snippet from "Design Patterns: Elements of Reusable OO software"

> 
> Part of an object's interface may be characterized by one type, and other parts by other types. Two objects of the same type need only share parts of their interfaces. Interfaces can contain other interfaces as subsets. - Design Patterns - Elements of Reusable OO software, pg 13
> 
> 
>