Diastole is a medical term that refers to the phase of the cardiac cycle when the heart muscle relaxes and fills with blood. It occurs between systole (contraction) and the next systole. 

Key Points:

• Definition: Relaxation of the heart muscle and filling with blood. 

Part of the cardiac cycle: Occurs between systole and the next systole. Function: Allows the heart to prepare for the next contraction by filling with blood. Related terms: Systole, cardiac cycle, ventricle. 

In other words, diastole is the pause between heartbeats when the heart rests and recharges. It is an essential part of the cardiac cycle and plays a crucial role in maintaining proper blood flow throughout the body.