Another person on AWAD sent me this take on thrall and has said I may paste it here:

"Cedric the Saxon was noble.
He had slaves (with some legal rights) called thralls.
The thralls had to wear a collar identifying their owner.
The Jester, Wamba, and herdsman, Gurth, were both thralls,
and wore collars so they could not run away without
getting caught. Evidently thralldom wasn't all bad.
Remember Gurth risked his life to get Cedric out of
captivity at hands of Front de Boeuf. "