What is an automatic watch?

1. An automatic is a mechanical watch whose mainspring is wound as a result of the wearer's arm motion.
2 - (Hampton Milleis). Is that the same as a hand-wound watch?
No. Hand-wound is a mechanical watch that the wearer winds by turning the crown by hand - (automatic swiss watch).
3. Why do they call it "automatic?"
Because instead of the wearer having to wind the watch to generate power, the watch winds itself "automatically" when worn.
4. What is the difference between an automatic and a self-winding watch?
Nothing. The terms are synonymous. Self-winding means that the watch winds itself.
5. Is that the same thing as a "perpetual" watch, like a Rolex Oyster Perpetual?
Right. Rolex refers to its automatic watches as "perpetuals." Automatic, self-winding and perpetual all mean the same thing: the watch winds itself. (A perpetual calendar, however, is something else.)
6. How does an automatic watch work?
The movement of the wrist and body causes the rotor, a metal weight attached to a winding mechanism, to pivot freely on its staff in the center of the movement. The rotor rotates back and forth in a circular motion at the slightest action of the wrist. The rotor's movement winds the mainspring, a flat coiled spring that powers mechanical watches.