DAU/MAU divides daily actives by monthly actives. A ratio of 0.5 means the average monthly user is active 15 days a month. Consumer social apps often cite ratios above 0.5; productivity tools sit around 0.3; weekly-cadence tools under 0.2.
The ratio is the most common stickiness benchmark. It's easy to game in the short term (push notifications) but hard to fake long-term, sustainable high stickiness requires a product that earns daily attention.