What does it mean that a method or class is abstract? (CoreJava)

Question :What does it mean that a method or class is abstract? (CoreJava)
Answer :An abstract class cannot be instantiated. Only its subclasses can be
instantiated. You indicate that a class is abstract with the abstract keyword
like this:
public abstract class Container extends Component {
Abstract classes may contain abstract methods. A method declared
abstract is not actually implemented in the current class. It exists only to
be overridden in subclasses. It has no body. For example,
public abstract float price();
Abstract methods may only be included in abstract classes. However, an
abstract class is not required to have any abstract methods, though most
of them do.
Each subclass of an abstract class must override the abstract methods of
its superclasses or itself be declared abstract.