How are antivenoms produced? Why are antivenoms an example of passive immunization?

Antivenoms are getting by the following process: the venom (antigen) is inoculated into other mammals, e.g., in horses; these animals make exact antibodies against the antigen; blood from the animals is collected and purified to get the antibodies; this antibody-containing material is the antivenom. When a human being is infected by the antigen the exact antivenom is given to him/her and the action against the antigen occurs.

Antivenoms might also be administered as a preventive measure and, as it is basically made of specific immunoglobulins against some antigen, the process is an instance of passive immunization.