Wheezing is a sort of whistling sound as air passes through a narrowed airway. This partial blockage, which stops oxygen getting into the bloodstream effectively, also causes shortness of breath and sometimes chest 'tightness'. In conditions like asthma and COPD, wheezing tends to come from the very small airways deep in the lungs. Sometimes, inflammation in the larger airways, the bronchi, can also make it hard for air to get through, causing wheezing. The medical term '-itis' means inflammation, and inflammation of the bronchi is called 'bronchitis'.
This is a companion discussion topic for the original article at https://patient.info/news-and-features/what-causes-wheezing