What is the definition of diastolic blood pressure?

Diastolic blood pressure refers specifically to the pressure in the arteries when the heart is in a resting state between beats, also known as the diastole phase of the cardiac cycle. This phase is crucial because it reflects the lowest level of pressure exerted on the arterial walls, allowing for the assessment of the heart's ability to adequately fill with blood and prepare for the next heartbeat.

In contrast, the other options do not accurately capture the essence of diastolic blood pressure. The pressure when the heart is beating corresponds to systolic blood pressure, which is the pressure exerted when the heart contracts. The average blood pressure during a heartbeat would involve both systolic and diastolic measurements, but it doesn't define diastolic pressure specifically. Lastly, pressure in the veins at rest does not pertain to arterial blood pressure and is not part of the standard measures used in assessing cardiovascular health.