Definition
Monthly active users (MAU) is the count of distinct users who used a product meaningfully in a month or a rolling 30-day window. It describes the size of the regularly engaged audience.
Formula
MAU = distinct users with at least one qualifying event in the 30-day period.
Reading it
MAU grows when you add users who stay. On its own it doesn't show how often they come; divide DAU by MAU for stickiness. A rising MAU with flat DAU means more occasional users, not deeper engagement.
How to measure it
Define the qualifying events, send them with a user ID, and chart monthly active users as a rolling window. See DAU, WAU and MAU.