Asthma is a chronic inflammatory airway disease characterized by recurrent wheezing, breathlessness, chest tightness and coughing due to narrowing of the bronchioles. There are different types of asthma including allergic, non-allergic, cough variant, occupational, exercise-induced, and medication-induced asthma. Diagnosis involves assessing symptoms, conducting pulmonary function tests like spirometry and peak flow measurements, and allergy testing to identify triggers.