Definition: The ecological footprint is to measure how we, humans, affect or impact on the environment for 1 year. An example may be measuring how much one person affects one hectare, how much of the resources of that area that person uses. It's not just 1 person, but other people affecting the other hectares in that area, and the combined impact of these people on a certain area and those individual hectares combined.
A farm may produce lots of crops, so I might eat lots through 1 year, so the amount consumed matches the number of crops produced. However, if I over consume and take too much of the food produced, my ecological footprint would be too large and have a large impact on the number of crops produced for everyone. The future sustainability of this food would be in question, leading to lack of food. If you are frugal and only eat small amounts, your ecological footprint would be very small and the sustainability of a farm would be high, lasting a long time.
This data from studying ecological footprints can inform us as to whether we are using too much of resources and so we can adjust our consumption so that our footprint is smaller and more sustainable. It's not just the individual that needs to think about their ecological footprint, but also countries, about whole areas of resources that we use, like crops in farms, fish in fisheries, trees in forests, water, tall buildings, cars, roads, land carbon, livestock – all those are resources that are used by us. We need to consider if there is enough of the resources to go round for all of us.