What is Abstract class

When I come across a term I don't understand, I find it helpful to do a Google and CodeProject search to see if there are any articles, wiki pages, blogs, etc, that detail the topic that I am interested in. In the case of a term that can be used outside of computing (e.g. abstract could refer to abstract thought, or a brief excerpt out of a book), I find it helpful to narrow the scope of my search by using a combination of "keyword" (if it's a keyword) and the language I'm interested in. Okay, so we've identified that you are going to query on Google (or Bing if that's your thing) using the phrase "abstract keyword c#". That should get you many hits.

Now most answers will stop at this point, but they are missing out on a very important part of your growth as a developer. What are the edge cases? In the case of abstract, is it possible to have a sealed abstract class (no - it wouldn't make sense)? What about if your abstract class doesn't have abstract methods - does it makes sense for it still to be abstract? As you progress as a developer, you will learn to ask questions like this - which will give you a more thorough understanding of the language.