There are several terms to describe halitosis: bad breath, morning breath, breathe odor, but they all usually mean the same, an unpleasant odor exhaled on the breath.
Breath odor is not a serious problem by itself, except in cases when it is caused by some other dental disease(s,) it is not however something that will improve our interpersonal relationships.
Most breath odor is caused by food particles left in our mouths. These remains are the breeding grounds for the halitosis bacteria. Among other causes there is poor oral health, periodontal disease, improper cleaning of dentures, and of course smoking. Sometimes it can be caused by stomach, lungs or bloodstream disease.