The overlap in concepts between MailChimp and CiviCRM means that they can readily be used in similar ways, but the overlap in terminology -- particularly when similar words are used in different ways -- can lead to confusion. The table below defines key terms from each system and relates them across systems when possible.

MailChimp CiviCRM
List. The body of subscribers who have opted in to hearing from you. No direct analog. CiviCRM itself is a database, and various flags determine what kinds of communications (if any) users wish to receive from you.
Group. A category within your list that organizes your subscribers according to their interests and preferences (or your interest in them). Getting started with groups. Static group*. The analogous entity in CiviCRM is the static group, often referred to simply as a group. Groups may be public or private. Users can manage their own membership in public groups. Only administrators may manage membership in private groups. A contact’s group membership record (his GroupContact record, in Civi-parlance) has a Status field which can be set to Added (current group member), Removed (former group member), or Pending (pending approval). View the groups a contact has been associated with (and the status of those associations) on the Groups tab of the contact summary screen.
Segment. A specific set of subscribers with common qualities. Often the commonalities are centered on some kind of engagement (e.g., opened January newsletter) or on a temporal component (e.g., new subscribers). Getting started with segments. Smart group*. The closest analogous entity is the smart group, which is essentially a saved search. Smart groups can be based on nearly any data point in the CRM (e.g., geography, giving history, etc.) and will be automatically updated as data change. (Note: technically, smart groups can be interacted with in a static way. For instance, Joe Smith of Nebraska could be manually added to the smart group “Florida members” despite his NE address. Such interactions can lead to unexpected results and are not recommended.)
Unsubscribed Members. Subscribers who have opted out of communications from a list. In Chorus America’s case, since there is only one List, members who unsubscribe effectively opt out of all bulk communications. How unsubscribes work in MailChimp. No Bulk Emails. Users who click the opt-out link in a CiviMail message will have this flag set and will not be included in any future bulk mailings. (They may still receive transactional mail, e.g., an event registration confirmation.) Note that this is different behavior from when a user clicks an unsubscribe link in a CiviMail message.
Unsubscribe. In CiviCRM, unsubscriptions are group-by-group. A user may unsubscribe from the Monthly Newsletter group but remain subscribed to the Conference Activities group. (See Static Group above.)
Do Not Email. A communication preference typically set by back-office staff. Prevents the contact from receiving bulk mail. Also prevents staff from sending individual mail via CiviCRM (e.g., New Email activity). Does not prevent the sending of transaction mail (e.g., receipts).
Deceased. Deceased contacts are automatically excluded from bulk mailings.
Do not SMS / Bad Email (Patron Mail). This field was renamed and overloaded as a way to track bounced emails from a marketing automation system in use prior to MailChimp. Since it is no longer in use, this field can be reverted to its original purpose.
On hold. A flag on email address records which indicates that no additional mail should be sent to the address (due to bouncing, etc.). In CiviCRM, contacts (rather than email addresses) are subscribed to groups, so if a contact has two addresses on file and one is flagged On hold, the other will be used in future mailings.

* For a group (static or smart) to be used in a CiviMail mailing, it must be of the Mailing List type.

Updated: 3-21-2019