First-Class Mail (FCM)
A mail class that includes all matter wholly or partly in handwriting or typewriting, all actual and personal correspondence, all bills and statements of account, and all matter sealed or otherwise closed against inspection. First-Class Mail comprises 3 subclasses: Post and Postal Cards, Letters and Sealed Parcels, and Priority Mail. Any mailable matter may be sent as First-Class Mail. First-Class Mail is a USPS trademark.