Social Security classifies the physical exertion requirements of jobs as sedentary, light, medium, heavy and very heavy. See 20 C.F.R. 404.1567. Social Security gives those terms the same meaning as they have in the Dictionary of Occupational Titles.
The light exertional level involves lifting no more than 20 pounds at a time with frequent lifting or carrying of objects weighing up to 10 pounds. Even though the weight lifted may be very little, a job is in this category when it requires a good deal of walking or standing.
Light exertional work is described in Social Security Ruling 83-10:
the full range of light work requires standing or walking, off and on, for a total of approximately 6 hours of an 8-hour workday. Sitting may occur intermittently during the remaining time. The lifting requirement for the majority of light jobs can be accomplished with occasional, rather than frequent, stooping. Many unskilled light jobs are performed primarily in one location, with the ability to stand being more critical than the ability to walk. They require use of arms and hands to grasp and to hold and turn objects, and they generally do not require use of the fingers for fine activities to the extent required in much sedentary work.