Immunization, or immunisation, is the process by which an individual is exposed to an agent that is designed to fortify his or her immune system against that agent. The material is known as an immunogen.
Vaccination and immunization
Immunization is the same as inoculation and vaccination in that inoculation and vaccination use a viable infecting agent like immunization does. Immunization is just the general term for vaccination and such things as what you gain from these proccess.
How does it work?
When the human immune system is exposed to a disease once, it can develop the ability to quickly respond to a subsequent infection. Therefore, by exposing an individual to an immunogen in a controlled way, their body will then be able to protect itself from infection later on in life.