Supermodular is a big word that means something that gets bigger and bigger as you add more and more things to it. For example, imagine you are playing with Legos and you have a big pile of them. If you start putting them together in a certain way, and each time you add a new Lego the pile gets bigger and bigger, then you are building something that is supermodular.
In math, we use this idea of supermodularity to talk about how things relate to each other. Let's say you have a bunch of different options for what to eat for dinner. Some options might be to have pizza, pasta, or salad. If you pick just one option, that's not very supermodular. But if you start combining options, like having pizza and pasta, or salad and pizza, then you start to see how things are getting bigger and more varied.
Basically, when things are supermodular it means that adding new things creates more diversity and more options, which can be really helpful in lots of different situations. It's like having a bigger and bigger toolbox, with more and more tools to help you solve different problems.