They are areas of chest wall projection that correspond to the four cardiac valves. In a clockwise fashion:
Aortic area: Second right parasternal interspace
Pulmonic area: Second left parasternal interspace
Erb’s point: Third left parasternal interspace (area of left ventricular outflow)
Mitral area: Apex (fifth interspace left midclavicular line)
Tricuspid area: Fourth to fifth left parasternal space, at times extending into the epigastrium/subxiphoid