Mastery Levels are useful for quickly visualizing student performance instead of having to scan individual accuracy percentages. It saves you time when analyzing results and provides a common language around student performance.
In order, the possible levels and their Raw Accuracy cutoffs are:
Mastery - 90%+
Excelling - 80-90%
Proficient - 70-80%
Passing - 55-70%
Struggling - 0-55%
These are set by default in Albert and can't, at this time, be customized.
A few places you can find Mastery Levels are:
On individual assignments:
On class dashboards: