According to the 백정 Wikipedia article, the etymology of 백정 is:
It consists of "Baek"(Korean: 백, Hanja: 白), which means 'no', and "Jeong(Korean: 정, Hanja: 丁)", which means a person without land.
In Wiktionary I cannot find these meanings for 백 or 정. Perhaps they stem from ancient usages of 백 and 정?
Perhaps the Korean Wiktionary has these meanings for 백 and 정? Unfortunately I cannot read Korean so I cannot check.
Note: The reference Wikipedia gives for this etymology is Kim, Joong Seop (2013). ""조선시대 백정"의 기원에 대한 역사사회학적 고찰" . [Articles : The Origins of the Outcast, Paekjong, in the Choson Period: The Socio-Historical Perspective Reconsidered].동방학지. 164: 140~141 – via 연세대학교 국학연구원(Yonsei Univ. Oriental Institute).