On a domain, how do you define new user properties

Question

I'm not sure the official name of these user properties so I'll explain them:

In Active Directory Users and Computers, if you right-click a user, hit "properties", than look under the "general" tab you'll see

• First name
• initials
• last name
• description
• office
• etc..

Is it possible to add a custom property, let's say, "twitter username", to each user? And what's the name of these properties?

Answer 1

After a lot of research, what I was looking for was extending the user schema

a good tutorial to do this is over here