Chronic cough means cough as a symptoms for-

Acute cough(<3 weeks) is most commonly due to a respiratory tract infection,aspiration event,or inhalation of noxious chemicals or smoke.Subacute cough (3-8 weeks) is frequently the residuum from a tracheobronchitis,such as in peussis or " post viral tussive syndrome".Chronic cough(>8 weeks) may be caused by a wide variety of cardiopulmonary diseases,including those of inflammatory,infectious,neoplastic,and cardiovascular etiologies.When initial assessment with chest examination and radiograph is normal,cough-variant asthma,gastroesophageal reflux,nasopharyngeal drainage,and medications (ACE inhibitors) are the most common causes of chronic cough. Ref:Harrison's medicine-18th edition,page no:283.