The actual wording is shok bisha erva.
There are different psaks as to what is erva. Some say (including the Chazon Ish, Chofetz Chaim and Rav Kook) that even below the knee (calf) is erva and you have to cover until the feet. Others say below the knee can be uncovered. But everyone agrees above the knee is erva and must be covered (in all movements and positions).