If customers find an app valuable, they will keep using it. That's retention. Retention reports visualize how often your customers return and engage with your application. You can use this data to track and measure if the changes you make to your app increase customer retention.
Cohorts are simply groups of customers that started using your app within a defined period of time. For example, all of the people who started using your app in January form a new customer cohort for that month. By displaying how often these cohorts return to your app, you can measure if changes you make to your app make it more or less valuable to customers. Cohorts are automatically grouped by day, week, or month, giving you the ability to see how your customer retention changes over time.
By default, retention reports display a recurring behavior (like logging in), but it can also show follow-up behavior. If two behaviors are related, then retention reports will show how often a person does one and then the other.
Just like Segmentation, retention reports also let you dig into more details to understand customer behavior at each step. For example, Zappos could create a funnel report to tell them how many customers bought shoes, then returned to buy again. Retention reports even allow you to see what percentage returned and bought shoes in a specific style, color, or size.