The term ENVELOPE ABBR. is an abbreviation for the components of an envelope, which is a flat paper container used to send documents or other items through the mail. The acronym stands for ENC (3 letters), which stands for Enclosure; ATT (3 letters), which stands for Attention; POB (3 letters), which stands for Post Office Box; STE (3 letters), which stands for Suite; and ATTN (4 letters), which stands for Attention.