There are two different kinds of lists in your HubSpot Marketing Hub Basic, Professional, and Enterprise account: active lists and static lists.
Active lists are dynamic, meaning that they automatically update and contacts will join the list whenever they meet the criteria and 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 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 at a certain time. 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. Then, you can look back at that static list later and see contacts who may no longer qualify for the criteria.