Final answer:
The bottom number in a blood pressure reading, known as the diastolic pressure, represents the arterial pressure of blood during ventricular relaxation or diastole. It is the lower value and typically around 80 mm Hg in a normal adult blood pressure reading.
Step-by-step explanation:
Blood pressure is measured as a ratio of two numbers: systolic pressure over diastolic pressure. The bottom number in a blood pressure reading, called the diastolic pressure, represents the arterial pressure of blood during ventricular relaxation or diastole. It is the lower value and is usually around 80 mm Hg in a normal adult blood pressure reading. The diastolic pressure indicates the pressure in the arteries when the heart is at rest between beats.