Simple Definition:

Disinfection is the process of removing harmful microorganisms [tiny living things that can cause disease] from surfaces, objects, or liquids, using chemicals or physical methods. It helps to prevent the spread of infections and keep things clean and safe. For example, wiping down a kitchen countertop with a disinfectant spray [spray that kills germs] kills bacteria and viruses, making the surface cleaner and less likely to make someone sick.

Very Simple Definition:

Disinfection means cleaning things to make them germ-free. For example, spraying a cleaner on a table to make sure there are no germs on it.