The term LTR stands for 'LETTER' and the crossword solutions ENV, SAE, and SASE are all acronyms related to letters. ENV stands for 'ENVELOPE', SAE stands for 'Self-Addressed ENVELOPE', and SASE stands for 'Self-Addressed Stamped ENVELOPE'. An ENVELOPE is a paper container used to send documents or other items through the mail, while a self-addressed ENVELOPE is an ENVELOPE with the sender's address already printed on it. A self-addressed stamped ENVELOPE is a self-addressed ENVELOPE with a postage stamp already affixed to it.