A watch movement is is the internal mechanism of the watch. There are two main categories of watch movements: mechanical and quartz.
A quartz movement uses electricity to vibrate a quartz crystal at a specific frequency. An electronic counter measures the vibrations in order to determine elapsed time. Quartz watches are very accurate, robust and durable. Most digital watches and cheap analog watches are quartz, as well as some high end watches. Almost all quartz watches with a second hand advance once a second to conserve power. All modern LCD digital watches are quartz watches. A very good quartz watch should be accurate to within 2 seconds a month.
A mechanical watch movement is a watch powered and regulated by mechanical mechanisms, driven by a spring. In a mechanical watch, the time is regulated by an oscillating balance wheel, with each oscillation advancing the watch by a fraction of a second. This is where the tick-tick-tick sound of a mechanical watch comes from. The higher the frequency of the oscillations, the more ticks per second a watch will perform, and the smoother it will sweep.
Mechanical watches are generally considered more interesting than quartz watches. They are, however, not nearly as accurate, robust or durable as a quartz watch, and there is no practical purpose to owning a mechanical watch over a quartz watch. Unless you find mechanical watches fascinating, you will be better served with a quartz watch. A mechanical watch that gains or loses less than 5 seconds a day is considered very good. The recommended service intervals for a mechanical watch are usually every 5 years. Mechanical watches are generally more expensive than quartz watches. Mechanical watches with a second hand almost always advance multiple times a second, and so appear to sweep smoothly, especially compared to a typical quartz watch. This is generally how you tell if a watch is mechanical, or quartz, from a glance.
Many mechanical watches are automatics/self-winding watches. This means that there is a mechanism (usually a mechanical rotor) that collects energy as you move around, and stores the energy in a spring, automatically winding your watch. If an automatic watch is not worn for a couple days, it will stop. If you have a non-automatic mechanical watch, you must wind your watch every day/few days. Automatic watches were popularized by Rolex in the 1930's. Rolex uses the term "perpetual" to refer to automatic watches.
There are types of watch movements that fall into neither or between these two categories. Electric watches (such as Accutrons) are neither quartz, nor mechanical. Somewhere in between these two categories, there are movements such as mecha-quartz, Kinetic/auto-quartz and Spring Drive.
Source from www.reddit.com/r/Watches/wiki/faq