Stad is a Swedish word that means "city" in English. A city is like a big town where a lot of people live and work. Stad is a special word because in Sweden, it has a specific meaning for places that have been given a certain level of importance and recognition by the government.
To be called a stad in Sweden, a place has to be big and have a lot of people living there. It also has to have important things like a hospital, a university, and a lot of stores and businesses.
Being called a stad is kind of like getting a special title that says "hey, this place is really important!" In Sweden, there are only a certain number of places that are stad and they are usually the biggest and most important cities in the country.
So, whenever you hear someone in Sweden say "stad," you know that they are talking about a really big and important city with lots of people and important things.