Nikkur (Hebrew: ניקור) is the process of making an animal kosher by removing chelev (forbidden fats) and the gid hanasheh (sciatic nerve).
[1] The basis for this practice is Leviticus 7:23, "You shall not eat of any fatty suet, whether from cattle, sheep, or goats."
[3] From the Biblical root נקר NQR meaning to "put out, bore, dig, gnaw" etc.
However, among Yemenite Jews, nikkur on the hind part of the animal is still practised.
[4] On the other hand, in countries like Israel, specially trained men are hired to prepare the hindquarters for sale as kosher.