Lyme disease. n. An inflammatory disease caused by a spirochete (Borrelia burgdorferi) that is transmitted by ticks and usually characterized by an initial rash followed by flulike symptoms including fever, joint pain, and headache.If left untreated, the disease can result in chronic arthritis and nerve and heart dysfunction.yme disease-an acute inflammatory disease characterized by a rash with joint swelling and fever; caused by bacteria carried by the bite of a deer tick. Lyme arthritis.