It means "the horns of a cow", and it occurs just once in the Torah. The Israelite people were being instructed to assign their priests, the Levites, towns as well as pasture land around them for the cattle they own and all their other beasts. "You shall measure off two thousand cubits outside the town (on each side)...that shall be the pasture for their towns (Bamidbar:35:5) What could be more appropriate than a sign that is reminiscent of a cow!! The note appears on the word ba'ama.
Incidentally, there is another place which also utilizes the horns of a cow and that is in the Book of Esther (7:9). Charvonah, one of the King's advisers, recommends to Achashverut to hang Haman on the gallows prepared for Mordechai. "Haman" which is the word which has the horns (karnay parah) shows that he received at human hands the same manner of death administered to beasts.
Indeed, one cannot overlook the fact that the rabbinic principle implied in carrying out Haman's sentence, "measure for measure", is the same word the Torah uses to "measure off" pasture land for beasts.
MICHAEL PLASKOW