The ratio of daily active users to monthly active users. It measures 'stickiness'—how often users are engaging with the product.
Why it matters: A DAU/MAU ratio over 20% is considered good, while over 50% is world-class (e.g., WhatsApp, Instagram). It proves the product is a daily habit.
In practice: If an app has 1,000 DAU and 10,000 MAU, the ratio is 10%. This means the average user opens the app 3 days out of a month.