A caravan is either a covered vehicle, like a wagon or a van, or a procession of vehicles. If you watch a parade with a long line of floats traveling one after another down the street, that's a caravan of floats.
The word caravan comes from the Persian karwan meaning "group of desert travelers." A caravan can be a large group of people traveling together in one long line. It's also the term used for a camper that has a living area in it. In history, pilgrims often traveled like this, lugging all of their belongings with them in caravans, or covered horse-drawn carriages. It's also a verb: caravan with your neighbors on a group road trip.