monkeyking

Abstract methods
An abstract method is a virtual or dynamic method that has no implementation
in the class where it is declared.
Its implementation is deferred to a descendant class.
Abstract methods must be declared with the directive abstract after virtual or dynamic.
For example,

procedure DoSomething; virtual; abstract;

You can call an abstract method only in a class or instance of a class
in which the method has been overridden.

这篇文章是从Delphi的Help文档里翻出来的。
比较简短，你先翻译着.