The Daily Active Users metric is commonly used for mobile products and just about every company calculates DAU numbers differently.
Daily active users (DAU) is the total number of users that engage in some way with a web or mobile product on a given day. In most cases, to be considered “active,” users simply have to view or open the product.
Monthly active users (MAU) is the aggregate sum of daily active users over a period of one month. In most cases, to be considered a “monthly active user,” a person has to open or view an app at least once in the period of one month. The ratio of DAU/MAU is typically a measure of ‘stickiness’ for internet products.
Here’s a great article for further info: