Graphene is a single layer of carbon atoms- basically a sheet of graphite one atom thick. It has real world applications, we use it at work in scientific research applications. Due to its cost, I cannot imagine that there is anywhere remotely near enough of it in a consumer product, like a tool battery, to actually make a significant improvement in functionality.
So, like said above, I'm guessing it's a marketing term. Like "titanium" scissors, and titanium, ceramic, billet, tactical... everything else