A Dyson sphere is a hypothetical megastructure that encompasses a star and captures a large percentage of its power output. The concept is a thought experiment that attempts to imagine how a spacefaring civilization would meet its energy requirements once those requirements exceed what can be generated from the home planet's resources alone. Because only a tiny fraction of a star's energy emissions reaches the surface of any orbiting planet, building structures encircling a star would enable a civilization to harvest far more energy.
I pirated this to check it out and enjoyed it so much that I bought it even though it's in Early Access and that's very very rare for me. I still haven't played it more though as I'm still waiting for it to come out of EA, looking very much forward to play it again.
edit: pirating this game is kinda funny to me, its a Chinese Dev. team so who knows if there are assets in the game that are not legit. I will probably buy it but I wouldn't shame anyone who did find another way to get it without purchasing it