Corpus Inscriptionum Etruscarum is a fancy way to say "a collection of writing on rocks and other things from a long time ago in a place called Etruria." Etruria was an ancient place in Italy where people called Etruscans lived a very, very long time ago.
The Etruscans were known for their art, religion, and writing. They wrote some important stuff on rocks, metal, and other things that lasted a really long time! Some of those things were discovered by people who like to learn about old stuff called archaeologists.
The Corpus Inscriptionum Etruscarum is a big book with all of the different things that the Etruscans wrote on, and it helps us learn more about them. It's like a big puzzle, and by putting all the pieces together, we can learn more about who the Etruscans were and what they did.