1) Enc 1) Accompaniment for a ms 2) Aid for an ed 3) Business reply encl 4) Business-letter enc 5) Business-reply encl 6) Certain encl 7) Common enc 8) Common RSVP enclosure 9) Convenience for RSVPing 10) Correspondence courtesy inits 11) Enclosure with a ms 12) Enclosure with an RSVP 13) Envelope encl 14) Freelance submission encl 1) Encl 
Abbreviation for Self-Addressed Stamped Envelope, usually sent with a query or manuscript so the editor or publisher can mail it back to the writer.
Stands for “self-addressed stamped envelope”, which publishers and agents often demand that you include when you submit them a manuscript (assuming you want the manuscript returned).