Population health is interested in what happens with the health of groups of individuals. It is an approach to understand this from different perspectives.
Not just how diseases, but also how the environment, economy, and society impacts on our mental and physical health. It seeks to understand what it does to us, how it restricts us in doing our day to day things and what is needed to make it better.
A short video by The King’s Fund explains briefly what this means in real life.