How is chest pain defined clinically?

Usually by the cause. Chest pain is discomfort located between the shoulders and abdomen. Cardiac chest pain, or angina, is usually described as pain or pressure feeling that occurs with activity, goes away with rest, and may be associated with shortness of breath, sweatiness, lightheadedness or nausea. Other causes of chest pain include gi, pulmonary or skeletal. Often it is characterized by being acute or chronic.
Good question. Chest pain is like a code word to get a 911 medical attention -- angina pectoris, a true cardiac pain is more like excruciating pressure, tightness, almost always accompanied by nausea, change of breathing or shortness or breath, cold sweat, and feeling like you are going to go out -- and if it's not relieved spontaneously then it's a heart attack!