1.nounA document, used primarily in trade finance and issued generally by a financial institution, in which the institution promises to pay debts up to a certain limit to be acquired by the beneficiary against delivery of documents specified in the letter.
2.nounThe minuscule or small letters (a, b, c, as opposed to the uppercase or capital letters, A, B, C).
"The strongest passwords are those which mix numbers and letters, upper case and lower case, and symbols."