This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
A class that is missing definitions for one or more methods. You can't thus create an object of that class. You must first create a subclass and provide definitions for the abstract methods. Unlike interfaces, abstract classes may implement some of the methods. Though you can't instantiate an abstract class, you can invoke its static methods.