A series of response options to research questions, representing degrees of a particular characteristic. The options are specifically ordered with sequential values (known as "ordinal") and have little overlap between neighboring options.
Usability professionals often use rating scales in questionnaires to collect data from users on subjective topics such as satisfaction and ease of use, but rating scales can also be used with more objective topics as well.
There are already a number of validated user satisfaction questionnaires which should be considered for this purpose. However, usability professionals often find they need to generate their own questions, many of which will use rating scales. In these cases, it is important to confirm both the reliability and validity of scales before using them.