Is the administration to humans of tetanus antitoxin that is produced in a horse in response to the inactivated tetanus toxin an example of passive immunity?
Yes, It is an example of passive immunity.
The definition of active and passive immunity:
Here tetanus antitoxin is introduced to human. This antitoxin is produced in a horse, The horse produced the antitoxin in response to inactivated tetanus toxin.
Human body get immunity against tetanus toxin, but the antitoxin is produced by the immune system of a horse . Human is using antibody (antitoxin) produced by someone else. So, this is an example of passive immunity.