In the field of law, a "garnishee order" or, more commonly now, "garnishment" is a court order for collecting a civil judgment. It is, therefore, one kind of "attachment" (= taking property from someone under the authority of a court order).

If (Defendant) A owes (Plaintiff) B a certain sum of money as a judgment in a lawsuit against A that B won, and A does not pay it to B, and (Garnishee) C owes A some money, B may have a court issue a garnishee order to C, and then C has to pay the money directly to B. (C is often A's employer but could be anyone who owes A money, including someone who had borrowed from A.)