Imagine there's a special club in Italy called the "Noble Club". This club is for people who come from really important and rich families. They're called "nobles". These nobles have special privileges and are treated very respectfully by other people.
The "Noble Club" is made up of a group of families who have been important in Italy for centuries. They have special titles like "duke" or "prince" that are passed down from generation to generation. They also have big houses and lots of money.
Back in the old days, these families used to have a lot of power and influence in Italy. They would help make big decisions about the country and how it was run. Nowadays, they don't have as much power, but they're still very important and well-respected.
So, the "corpo della nobiltà italiana" is just a fancy way of saying "Italian Noble Club". It's a group of really important and rich families in Italy who have been around for a long time and still have a lot of influence and respect.