What is the loophole in the 13th Amendment that allows slavery to continue in a different form?

Several different things make up a culture like, how the people worship, their form of government, geography, and trade. religion is one of the most important things to a culture, it defines peoples life. their different beliefs form into festivities and events that merge with their culture. people that practice hinduism see cows as gods, so no doubt they would celebrate cows, and these celebrations would definitely merge with their culture. those that are buddhist live life trying to reach a certain level of peace, so no doubt would they change things in their life in order to correspond with their religion.