Monthly Active Users (MAU) is defined as the number of unique active users within a month. A user is counted as active when he or she takes a certain action, this could be logging in or performing a transaction.
Especially in early stages, when revenue streams are just starting, MAU can give insight about growth and expected future revenue. For companies that earn their money through advertisements shown to their users, MAU provides the user base that can be monetized.
This metric can be calculated for every other time frame. Another common version is Daily Active Users (DAU).
The sum of all unique active (i.e. performing a certain action) users of a month gives the Monthly Active Users
Σ unique active users
In January, 450 different people logged into the platform of a SaaS company.
450 different people