The phrase "collapsing trachea" refers to a condition where the airway in your throat, called the trachea, becomes narrow and collapses, making it difficult to breathe. Full definition
Factors that tend to enable clinical signs of collapsing trachea include: (web-dvm.net)
In the animal with a cough or any other breathing problem, the veterinarian will use a number of tools to determine if the cause is heart disease, lung disease (such as collapsing trachea) or both (which is often the case in older dogs). (vetmed.tufts.edu)
Let's go over the basics about what you should know about collapsed trachea in dogs Owners whose dogs suffer from tracheal collapse can tell you that when it happens, it's a sound that fills you with dread and fear. (petguide.com)