Active Directory groups can be imported using either a Static mapping strategy or a Dynamic one (Active Directory works for both).
The only difference is in the attribute defined on the corresponding Active Directory entry:
The Static mapping strategy defines a "member" multi-value attribute on the group entry containing user DNs of the group members
The "Dynamic" configuration defines a "memberOf" multi-value attribute on the user entry containing group DNs of the groups the user is a member of.
Active Directory supports both configurations, so you can choose the one which fits your organization's structure.