Lung cancer is a type of cancer that begins in the lungs, most commonly in the cells lining the air passages. It occurs when abnormal cells grow uncontrollably, forming tumors that can interfere with breathing and spread to other parts of the body. The two main types are Non-Small Cell Lung Cancer (NSCLC) and Small Cell Lung Cancer (SCLC). Smoking is the leading cause, but non-smokers can also develop it due to factors like pollution, radiation, and genetic predisposition.