What does “contract” of a class mean

Question

I am reading the book The Java Programming Language. In the chapter which explains overriding method, it says:

Making an override met

Answer 1

The contract of a class or interface, in Java or any other OO language, generally refers to the publicly exposed methods (or functions) and properties (or fields or attributes) of that class interface along with any comments or documentation that apply to those public methods and properties.

In the case of the relationship between a class and subclass, any protected methods or properties would be considered "publicly exposed," in the sense that they are exposed to the subclass.