A segment is a group of users, grouped by defined criterions, such as user profile properties, actions taken. For example, a segment can be users who visited a website for the first time in the past 30 days. A more complex segment could be users who live in San Francisco, were acquired via an Instagram campaign in May, purchased 3 or more times from January till April. Once you’ve identified your target segments, you can create them and start mapping your segments to the corresponding campaigns. You can also analyze segments over time to understand how a segment behaves in response to your marketing initiatives.