Velocity in Scrum, actually

In Scrum it is considered a good idea for teams to know about the progress they have been making. It can be one parameter (of several) to take into account when considering the inherently uncertain future. Teams often use ‘Velocity’ as an indicator of progress. As the term is not even mentioned in the Scrum Guide we’d better consider carefully how to apply it in accordance with Scrum’s foundational principles.