Usability in terms of “web usability” is basically the ability or ease for a person to use a website or web application to reach a desired goal. Such as, how easy is it to use Travelocity.com to book a flight or check your bank account balance using Chase.com.
When designing and building a website you should always have the core functionality at the helm driving how you design and develop to get the user from the front page to the end of the desired reaction. To do this, you not only need to know what you want the user to do, but how users interact with the web.
Usability of a website or web application depends on five factors:
- Learnability: How easy is it for users to accomplish basic tasks the first time they encounter the design?
- Efficiency: Once users have learned the design, how quickly can they perform tasks?
- Memorability: When users return to the design after a period of not using it, how easily can they re establish proficiency?
- Errors: How many errors do users make, how severe are these errors, and how easily can they recover from the errors?
- Satisfaction: How pleasant is it to use the design?