Tourbillon means 'whirlwind' in French
First designed in 1790 by Abraham Louis Breguet
Basically Breguet designed this to compensate for gravity. A 'standard' detached lever escapement is oscillating but always / only on one position.
Hence Breguet decided to compensate for that and mounted the escapement in a caraselle that rotates once per minute.
Therefore allowing gravity to be effective in all positions of the balance wheel
Here's another way to look at it.
Before wrist watches, men had pocket watches. Being kept in the pocket, it pretty much stayed in only one position all day long. And because of the basic design of the movement, gravity would have a bad effect on accuracy as long as that watch stayed in only that one position. This prompted Mssr. Breguet to invent the tourbillon. If you observe a tourbillon on YouTube, you'll notice the whole tourbillon cage turns around once every minute. This rotating of the balance simulates the effect of the movement turning in all sorts of positions, even while the watch itself may not be moving at all. In essence: the tourbillon was designed to negate gravity.
Wrist watches, however, do not need tourbillons. As pocket watches evolved into wrist watches, design evolved as well. Better and more modern materials were developed. Gravity was no longer an important factor in the watch's ability to remain accurate. But watchmakers still kept up the practice of learning how to build them as a matter of pride. It is a way of marking the difference between a watchmaking artisan and a regular watch assembler.