A sharecropper is a tenant farmer, someone who works land that's rented from its owner. Typically, a sharecropper will pay the landowner with part of the harvest, rather than money.
The word sharecropper, an American invention from the 1880s, comes from the fact that these farmers would share their crops in return for the use of the land. This system became widespread in the southern states of the US after the Civil War, and it was in large part influenced by the end of slavery. There were both black and white sharecroppers well into the 1950s.