Sedentary: Spend most of the day sitting (e.g. bank teller, desk job)
Lightly Active: Spend a good part of the day on your feet (e.g. teacher, salesman)
Active: Spend a good part of the day doing some physical activity (e.g. waitress, mailman)
Very Active: Spend most of the day doing heavy physical activity (e.g. bike messenger, carpenter)