In this lesson we will focus on one word: domain. This word is loaded with all kinds of confusion. The problem lies not in the word itself but its (over)usage in certain areas. Simply put a domain is a boundary that defines something (or contains it if that makes you feel better). So why should you care? Well, the ability to adequately KNOW what a domain is and actually KNOW how to apply its principles is fundamental to your success in the database world.