LLL: Acronym for the left lower lobe (of the lung). The left lung has but two lobes. The other lobe is the left upper lobe (LUL). The right lung has three lobes: the right lower lobe (RLL), the right middle lobe (RML), and the right upper lobe (RUL). The reason why the right lung has three lobes whereas the left lung has only two is not known but a... Found on http://www.medterms.com/script/main/art.asp?articlekey=7177