Trying to think of best way to explain it...It's basically health promotion and prevention. Thinking of the health of the community as a whole. So, say, promoting vaccinations, for example. Trying to reduce infant mortality. Finding ways to deal with chronic diseases that affect large populations of people, like diabetes, heart disease, etc. So looking at health on a bigger scale as opposed to a medical doctor seeing individual people and treating them. (If anyone else on here is in public health and wants to offer a better explanation, go for it!)