A segment in an electrocardiogram is the region between two waves. PR segment begins at the end of the P wave and ends at the onset of the QRS complex. ST segment starts from the end of the QRS and terminates at the onset of the T wave. TP segment is between the end of the T wave and the beginning of the next P wave. It is the true isoelectric interval in the electrocardiogram.
An interval in an electrocardiogram includes one segment and one or more waves. PR interval starts at the beginning of the P wave and ends at the onset of the QRS. It denotes the conduction of the impulse from the upper part of the atrium to the ventricle. QT interval starts at the onset of the QRS and ends at the end of the T wave. It denotes the electrical systole of the heart.