Understanding: The human ability to compare emotion to its symbolical representation. Linguistically and factually, understanding relates to intelligence. We say "I understand" when what we think and what we feel appears to be more or less congruent. A full understanding requires a (form of) language and a (form of) emotion to reach a (form of) balance. Like computers (see Artificial Intelligence) we can say things without understanding, by just repeating patterns that we deem beneficial or probable rather than credible. We say what we mean when we express our feelings as we understand them. The complex interplay between what we perceive, feel, think and understand, say and mean, say and do defines whether or not we speak truthfully. (See truth.

Usability: Usability is tied to what every person or "User" is “used to”. If somebody successfully completes their tasks, the product or service’s usability is considered high. If not, it is considered low. A designer can and should know theoretical usability standards. They can and should test the practical usability of a product or service. The only way to find out if a product is useable or not is to test it. The only way to be sure if it really is used or not is by releasing it. A useable product will be perceived as beautiful over a longer period of time, even if it has graphic deficiencies. Design Positivism suggests that usability will become an objective science with a set of laws carved in stone. In reality, usability rules are in constant flux as a medium evolves and is used by more people.

User: Human using an Interface. Also known as “person”, "client", "customer" or "client of client", "customer of customer”, “reader”, “shopper” or whatever you may call the person that uses your product. The word itself has a bad rep because of drug addicts. Some claim that human, person, "I", "you" or "they" would be a more appropriate word. Others say "user" is an abstract, technical term, very well understood and without magical impact on the design of a product. The discussion on how to call the user something other than user is a classic case of Everybody is always somewhat right.