What is a medina?

The short answer

The Arabic word for "city."

In Morocco, it refers to the old walled city — the original urban centre, built before cars, with narrow streets, mosques, markets, and residential quarters packed inside defensive walls. Every major Moroccan city has one. The modern city (ville nouvelle) was built outside the walls during the French protectorate, starting in 1912. When people say "the medina," they mean the old city inside the walls.