To inactivate is to render microorganisms unable to multiply — to destroy their capacity for growth and reproduction, whether or not every cell is technically killed. Heat inactivates pathogens in pasteurisation; disinfectants inactivate viruses on surfaces; stomach acid inactivates many ingested microbes. The term is deliberately functional: food safety cares whether organisms can grow and cause harm, not about philosophical definitions of microbial death. Validation of any inactivation step — the pasteuriser’s time-temperature, the sanitiser’s concentration-contact time — must demonstrate a defined log reduction of the target organisms. “Inactivated” is also the status of killed vaccines: pathogens rendered unable to replicate but still able to train immunity.