Reusability vs. Usability — What's the Difference?

In computer science and software engineering, reusability is the use of existing assets in some form within the software product development process; these assets are products and by-products of the software development life cycle and include code, software components, test suites, designs and documentation. The opposite concept of reusability is leverage, which modifies existing assets as needed to meet specific system requirements.

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. In software engineering, usability is the degree to which a software can be used by specified consumers to achieve quantified objectives with effectiveness, efficiency, and satisfaction in a quantified context of use.The object of use can be a software application, website, book, tool, machine, process, vehicle, or anything a human interacts with.

To use again, especially after salvaging or special treatment or processing.

Capable of being used

The property or degree of being reusable.

Fit for use; convenient to use

The state or condition of being usable.

The degree to which an object, device, software application, etc. is easy to use with no specific training.