Active users are people who use a certain website or app regularly. Imagine you have a toy box with lots of toys inside. Now, let's say you like to play with your toy box every day. That would make you an active user of your toy box! Similar to this, active users of a website or an app are people who log in or use it frequently. The more often they use it, the more active they are! It's important to track active users because it helps people who own the website or app understand how many people are using it every day.