Monthly active users or MAUs refer to the number of users who engage in some way with your app at least once in a month. MAUs are a KPI used to measure the health of an app.
In many cases, to be considered active, users need only view your app or launch it on a monthly basis. Although it would be ideal if that activity involves engaging with your app in a meaningful way, many companies choose to simply base the MAU metric on opening the app.
Monthly active users are typically your active users and champions – the ones who are most engaged with your product and most likely to evangelize your app to non-users.