MET stands for Metabolic Equivalent. It's a unit used to measure the amount of energy the body expends during physical activity compared to the resting metabolic rate which, expressed as oxygen consumption, is 3.5 mL O2 per kg bodyweight and per minute.

At rest, MET = 1.

Different activities require different levels of energy expenditure. The higher the intensity of the activity, the greater the MET value.

The 7.5 MET hours/week refers to activities that require energy expenditure of at least 7.5 MET the durations of which accumulate to at least one hour per week.

Running at 5 mph (8 km/h) is roughly equivalent to 7.5 MET