Final answer:
In the cardiac cycle, systole refers to the phase where the heart contracts, specifically when the ventricles contract to push blood out of the heart.
Step-by-step explanation:
During the cardiac cycle, the heart alternates between two phases: systole and diastole. Systole is the phase of the cardiac cycle when the heart muscles contract. Specifically, ventricular systole occurs after the atria relax (atrial diastole) and involves the ventricles contracting to push blood out of the heart. This contrasts with diastole, when the heart muscle is relaxed and the heart chambers fill with blood.