Monthly active users (MAU) is a key performance indicator (KPI) used by social networking and other companies to count the number of unique users who visit a site within the past month. Websites generally recognize monthly active users via an identification number, email address, or username.
MAU helps to measure an online business’s general health and is the basis for calculating other website metrics. MAU is also useful when assessing the efficacy of a business’s marketing campaigns and gauging both present and potential customers' experience. Investors in the social media industry pay attention when companies report MAU, as it is a KPI that can affect a social-media company’s stock price.