Usability can be described as the capacity of a system to provide a condition for its users to perform the tasks safely, effectively, and efficiently while enjoying the experience.
If something is useful, it can be used to achieve a particular objectivenot influenced by personal feelings or opinions in considering and representing facts.. DesignersPeople who are engaged in the production of functional products, services and systems will, generally, aim to deliver useful products. Usable, on the other hand, refers to the ease of use for a particular product and the more usable a product is the more likely it is that it will be used.