Short answers, pulled from the story.
Mare Nostrum is Latin for "Our Sea." It was the term used by the Roman Empire to refer to the Mediterranean Sea, reflecting Rome's claim as the only state in history to have controlled the entire Mediterranean coastline.
Romans first used Mare Nostrum to refer to the Tyrrhenian Sea after their conquest of Sicily, Sardinia, and Corsica during the Punic Wars with Carthage. By 30 BC, as Roman dominion extended from the Iberian Peninsula to Egypt, the term came to cover the entire Mediterranean Sea.
Benito Mussolini used Mare Nostrum as fascist propaganda in a similar manner to Adolf Hitler's use of Lebensraum. He declared "the twentieth century will be a century of Italian power" and built one of the most powerful navies in the world, aiming to make the Mediterranean an "Italian lake" and expand an Italian Empire from Egypt to eastern Kenya.
Operation Mare Nostrum was a military and humanitarian operation authorized by the Italian government following the 2013 Lampedusa migrant shipwreck. Its purpose was to rescue migrants crossing the Mediterranean Sea and to arrest human traffickers.
Mare Nostrum is a best-selling novel by Spanish author Vicente Blasco Ibáñez, published in 1918. A film based on the novel was released in 1948.
Following the unification of Italy in 1861, nationalists who viewed Italy as the successor state to the Roman Empire began calling for an Italian colonial empire, particularly during the Scramble for Africa in the 1880s. They argued Italy needed control of the Mediterranean to avoid being, in their words, "suffocated" in it by rival powers.