Health policy must tackle the social and economic determinants of health. Poor social and economic circumstances affect health throughout life. Social gradient would be best depicted by a ladder.
When thinking about health inequalities people often use the analogue of the ladder to show how the gradient of worsening health outcomes affects all people in society except those at the very top. This leads to the second part of the answer. health follows the social gradient. Those second from the top have worse health than those at the top, and so on, all the way down the social hierarchy.