Renovatio Imperii Romanorum is a big, fancy Latin phrase that means "The Renewal of the Roman Empire".
Long, long time ago, the Roman Empire was a very powerful kingdom that conquered many other lands and spanned over many countries. They had a great civilization with many achievements like advanced architecture, engineering, language, and even their own version of democracy. But over time, the Roman Empire started to weaken and many of their lands were lost to other countries.
So, some people in the Middle Ages, (a really long time ago), thought it would be a good idea to try to bring back the former glory of the Roman Empire. They wanted to start a new empire that would be just like the old one, modernized yet still have the characteristics that made Rome so great.
The idea behind the Renovatio Imperii Romanorum was to revive the Roman Empire - its culture, values, and power, but it wasn't as easy as it sounded. People had to study and learn from ancient texts, architecture, and art because everything from the old empire had already been lost or broken apart.
Many people tried to bring back the Roman Empire over time, including the Byzantine Empire, the Holy Roman Empire, and even Napoleon Bonaparte. But none of them were able to restore the true glory of the old Roman Empire. The idea of Renovatio Imperii Romanorum is still remembered today as an attempt to rebuild the past and regain what was lost but maybe it's better to see it as an inspiration to learn from history than to try to relive it exactly.