Systole is the contractile phase of the cardiac cycle and diastole is the relaxation phase of the cardiac cycle.
Cardiac Cycle
Ventricular filling: Mid-to-late ventricular diastole (includes atrial systole, P-Q interval)
Ventricular systole: isovolumetric contraction and ejection phase (Q-T interval)
Quiescent phase: isovolumetric relaxation in early ventricular diastole until atrial contraction (end of T wave to beginning of next P wave)