Standard chatter profiles in Salesforce

Chatter profiles are only for users with the Chatter Free or Chatter External user licenses, and allow users to log in to Chatter only.

Chatter Free User
Access all standard Chatter people, profiles, groups, and files.
Chatter External User
Access groups they've been invited to and interact with members of those groups.
Chatter Moderator User
Access same data as Chatter Free users. But they can also

1. Activate/deactivate other Chatter Free users and moderators.
2. Grant/revoke moderator privileges.
3. Delete posts and comments they can access.