Sahih International: And [recall] when Moses said to his people, "O my people, indeed you have wronged yourselves by your taking of the calf [for worship]. So repent to your Creator and kill yourselves. That is best for [all of] you in the sight of your Creator." Then He accepted your repentance; indeed, He is the Accepting of repentance, the Merciful.(2:54)
What is the meaning of "and kill yourself"?