1) A class of lipoproteins responsible for transport of cholesterol to extrahepatic tissues. They are formed in the circulation when very-low-density lipoproteins are degraded first to intermediate-density lipoproteins and then to LDL by the gain and loss of specific apolipoproteins and the loss of most of their triglycerides. LDL are taken up and catabolized by both the liver and extrahepatic tissues by specific receptor-mediated endocytosis. (Dorland, 28th ed)

2) Low-density lipoprotein (LDL) is a lipoprotein that carries cholesterol around the body, for use by various cells. LDL transports cholesterol to the arteries and increased levels are associated with atherosclerosis, and thus myocardial infarctions and strokes. This is why cholesterol inside LDL lipoproteins is called bad cholesterol. (from Wikipedia)