Contact
Segments for grouping people, and the inbound requests arriving from public pages.
Contact covers two related things: segments, which group members for targeting, and contact requests, which arrive from the organisation's public pages.
Segments
A segment is a named, coloured group of members. Membership is explicit, so a segment survives changes to a member's status or affiliation — useful for the groupings a filter cannot express: a committee, a cohort, past speakers.

Segments are a first-class campaign audience. Selecting several mails everyone across them once — a member in three segments receives one email, not three.
Contact requests
Enquiries submitted from public pages land here rather than in an inbox, so they carry a status and are visible to the whole team.

Use cases
A committee mailing list that stays correct
Put the committee in a segment. Membership does not drift when someone's dues lapse or their affiliation changes, and the list is visible to every administrator rather than living in one person's mail client.
Suppression is separate
Someone unsubscribing is recorded on the do-not-email list, which is checked at send time regardless of segment or audience. Removing a person from a segment is a targeting decision; suppression is a consent decision, and the two never overwrite each other.