IPA: /ˌɪm.jə.nəˈzeɪ.ʃən/
KK: /ɪˌmjunəˈzeɪʃən/
The process of making a person or animal immune to a disease, usually by giving them a vaccine.
Vaccination is an important part of childhood immunization programs.
Immunization → It is formed from "immunis" (from Latin, meaning exempt or free from) and the suffix "-ation" (indicating a process or action). The word "immunization" refers to the process of making someone immune or exempt from a disease.
Think of being 'exempt' ('immunis') from illness through a 'process' ('-ation') — that's what immunization means.