Usability testing involves testing a design with a representative group of users to determine its usability. Users are usually observed completing tasks and it can be done for a variety of designs. It is often repeated from the early stages of development to the release of a product.
Usability testing can uncover design flaws you might otherwise overlook. When you watch how test users behave while they try to execute tasks, you’ll get vital insights into how well your design/product works. Then, you can leverage these insights to make improvements.