Hello, this is a common expression which means being able to enjoy the benefits of two different opportunities/situations/things at the same time. For example, if Tom is going to university, but has decided to live at home with his parents while doing so, we could say, "Tom's getting an education and free room and board; it's the best of both worlds." because he is enjoying the best of university and home. Hope that helps!

It means you get the benefits from two contrasting situations at once. For example many people do not want to live in the countryside because it is far from the shops and conveniences of modern life. But many people do not want to live in the city because it is dirty, ugly and noisy. So if you live somewhere in the countryside that was very well connected, you could say you have the best of both worlds - the advantages of both the countryside and the city, without the disadvantages of either.

In addition to Olivia's and Maddie's excellent answers we also say "The worst of both worlds", which is the exact opposite.