Social Security characterizes work as sedentary, light, medium and heavy.  The simplified definitions are as follows:

Sedentary:  Requires the ability to sit up to six hours in an eight hour work day, lift light objects such as files and paperwork frequently during the day, and objects weighing up to 10 pounds occasionally during the day.

Light:  Requires the ability to stand up to six hours in an eight hour work day, lift up to 10 pounds frequently and up to 20 pounds occasionally.

Medium:  Requires the ability to stand up to six hours in an eight hour work day, lift up to 25 pounds frequently and 50 pounds occasionally.

Heavy:  Same standing as light and medium, lifting heavier than medium.