The ST segment is a part of an electrocardiogram (ECG or EKG) that represents the period between the end of ventricular depolarization and the beginning of ventricular repolarization. It is crucial for assessing the heart's electrical activity and can indicate various cardiac conditions when analyzed. Abnormalities in the ST segment, such as elevation or depression, may suggest issues like myocardial ischemia or myocardial infarction. Healthcare professionals often examine the ST segment to diagnose heart problems and monitor the effectiveness of treatments.