One view of medical care is that if something is wrong, you can go to the doctor to get better. The medical definition of health is often just the absence of a particular disease.
However, there is another view of health and wellness – this is the view that sees wellness as a combination of several dimensions, and sees the interaction of the person and their environment. In this view, we not only want to cure an illness, we want to prevent it from happening if possible. This is the public health model of health.
We can think of prevention as a behavior that eliminates or lowers the chances that a disease will happen in the first place (primary), or behaviors that lead to a disease being discovered early and thus treated early (secondary).
Examples of primary prevention are vaccination, wearing condoms, putting on sunscreen and hand washing. Examples of secondary prevention are Pap smears, mammograms, and other screening tests.
Here are a few more ideas for preventing disease – https://www.nih.gov/health-information/disease-prevention-toolkit.