1. the twelfth letter of the English alphabet: from the Greek lambda, a borrowing from the Phoenician. 2. any of the speech sounds that this letter represents, as, in English, the (l) of love.

l, twelfth letter of the alphabet. Ancestors of this letter were the Semitic lamedh, which may derive from an earlier symbol representing an ox goad, and the Greek lambda (λ). The form appearing on the Moabite Stone was rounded. Other Greek forms were found in early inscriptions from Attica and Corinth.

L is usually short for “loss.” If you “take an L” it means you're taking a loss. This can be a literal loss, as in you losing a pickup basketball game or, or it can be a figurative loss, like you not getting to go to a party.