Definitions of Usability

Expert usability review.

Review identifies the places where people are likely to get stuck and the things that will confuse them.

Usability testing.

Shows where they get stuck and confused.

Usability issue.

The meeting with usability professional and the client's team. The meeting discuss about problems which was found that are likely to cause users grief and help them decide which ones are most important to fix and how best to fix them.

Interaction design

Deciding what happens next when the user clicks, taps, or swipes.

Information architecture

Figuring out how everything should be organized.

Useful: Does it do something people need done?
Learnable: Can people figure out how to use it?
Memorable: Do they have to relearn it each time they use it?
Effective: Does it get job done?
Desirable: Do people want it?
Delightful: Is using it enjoyable, or even fun?

Based on the Steve Krug's book "Don't make me think"