What is the difference between absolute and relative pressure?

Absolute pressure is the measured atmospheric pressure.

Absolute pressure is not corrected to sea-level conditions.

To compare pressure conditions from one location to another, meteorologists correct pressure to sea-level conditions (referred to as relative pressure, or pressure relative to sea level).

Because the air pressure decreases as you rise in altitude, the sea-level corrected pressure (the pressure your location would be at if located at sea level) is higher than your measured pressure if you live above sea level and lower than your measured pressure if you live below sea-level.

Relative pressure is the atmospheric pressure corrected to sea-level conditions.

To compare pressure conditions from one location to another, meteorologists correct the measured pressure (referred to as absolute pressure) to sea-level conditions. Because the air pressure decreases as you rise in altitude, the sea-level corrected pressure (the pressure your location would be at if located at sea level) is higher than your measured pressure if you live above sea level and lower than your measured pressure if you live below sea-level.

Relative pressure is larger than absolute pressure unless you live at or below sea level.