Active lists automatically update with contacts joining it whenever they meet the criteria. Static lists are a snapshot of a group of contacts who meet a certain set of requirements when the list was created and saved. They require manual updating
Lists can only be used for contacts. However, in addition to property values, lists allow you to segment your contacts with other filters, such as page views, form submissions, and email interactions.
Active lists
Active lists automatically update with contacts joining it whenever they meet the criteria. They then will also leave the list when they no longer meet the criteria.
For example, an active list would be valuable when you have an email campaign to a particular subset of your contacts running over time, and always want the list to update with new contacts who meet the criteria.
Static lists
Opposite to active lists, static lists do not update as new contacts meet the criteria. Instead, they are a snapshot of a group of contacts who meet a certain set of requirements when the list was created and saved. Contacts can be manually added and removed from static lists.
A static list can be helpful to gain an understanding of contacts who met a certain criteria on a particular date. You can look back at that static list later and see contacts who may no longer qualify for the criteria.