What is Usability (UX)?

Usability is the degree of ease with which products such as software and Web applications can be used to achieve required goals effectively and efficiently. Usability assesses the level of difficulty involved in using a user interface. Although usability can only be quantified through indirect measures and is therefore a nonfunctional requirement, it is closely related to a product’s functionality.:

A usable interface has three main outcomes:

It should be easy for the user to become familiar with and competent in using the user interface during the first contact with the website. For example, if a travel agent’s website is a well-designed one, the user should be able to move through the sequence of actions to book a ticket quickly.
It should be easy for users to achieve their objective through using the website. If a user has the goal of booking a flight, a good design will guide him/her through the easiest process to purchase that ticket.
It should be easy to recall the user interface and how to use it on subsequent visits. So, a good design on the travel agent’s site means the user should learn from the first time and book a second ticket just as easily.

Importance
1) Increasingly critical for product success
2) Users expect systems to work but will chose those that are easier to use
3) Industry looking for SW engineers who can provide great “user experience