Dynamic Filters automatically add members to a group when those members meet certain parameters that you define. You can create a Dynamic Filter that populates a group with all students in a particular grade, with all constituents of a given gender, with all alumni of a specified class year, and so on.
Contrast using Dynamic Filters with the other way to add members to a group, which is by explicit selection. This is when you manually search Constituent Manager for individual users, and add them to the group one-by-one.
You can stack various selection criteria together in a single Dynamic Filter, thereby making a very complex set of parameters that constituents must meet in order to be filtered into a group.
For more information, see the Knowledge Base article, Creating dynamic filters with profile data.
When to Filter and When to Select
Explicit Selection may be appropriate when populating an Academic Class, for instance, as the members of a given English class probably will not all fit the same sorting criteria - students may come from different class years, different genders, etc, so it would be difficult to create a filter that accurately captures all of them. A Dynamic Filter is more useful and appropriate when you want to use a group to manage a particular class of users, such as all 10th graders, or all Faculty (or, as we'll see, send an eNotify message to such a collection of users).
The difference between a Dynamic Filter and explicit selection is that if members in a group are explicitly selected, that membership roster will never change. If you use a Dynamic Filter to populate a group, then the members of that group can change without your having to do anything. For instance, a group called "10th Graders" that is explicitly populated will always contain the same students, year after year. When those students progress to the 11th grade, the list would need to be reconstructed, as it would no longer accurately describe the students it contains. If the same list were constructed using a Dynamic Filter whose criteria were set to "Students in Grade 10," then the list would never have to be updated. As students moved out of Grade 10 (as reflected by the information in Constituent Manager) they would fall off the list, while new students who move into Grade 10 would be automatically added.
Dynamic Filters in eNotify
Dynamic Filters can be used not only to create groups in Group Manager, but also mailing lists in eNotify. In either case, any constituents who match the defined criteria will be included in the group, or will be added to the eNotify mailing list. (See the Knowledge Base article, Configuring dynamic filters in eNotify for more details.)
Note that, in addition to creating a list using a Dynamic Filter, you can also use a group from Group Manager as the basis of a mailing list. If you use a group which is populated via a Dynamic Filter to add members to a mailing list, this is exactly the same as creating a mailing list based on the same Dynamic Filter. In other words, if a group in Group Manager and a mailing list in eNotify are both configured with identical Dynamic Filter criteria, then they will be equivalent and will always have the same members.