Chronograph - is a device used to measure time intervals lasting from fractions of a second up to 12 hours. In other words, it is a stopwatch within a watch.
Chronometer - A chronometer is a watch that has been tested and certified to meet certain precision standards by the COSC (Official Swiss Chronometer Control) in Switzerland.
Automatic Watch - A watch that contains a mechanical watch movement that is wound by the motion of the wearer's wrist. Because the movement is mechanical and can consist of over 100 working parts, these watches are appreciated for their craftsmanship.
Complications - Used when referring to mechanical watches, the term “complications” indicates special functions that the watch is able to perform and display beyond the simple hours, minutes, and seconds. A GMT is an example of a complication.
GMT - GMT (Greenwich Mean Time) is a watch that displays an additional time zone as well as your home time. This feature can be displayed with an independent hour hand or with a fixed hour hand (makes one revolution around the dial per day).
Tachymeter - A tachymeter is typically positioned on the bezel and generally only found on chronographs. This feature can be used to measure speed while timing over a given distance.
Perpetual Calendar - A perpetual calendar is a mechanism that automatically considers the varying number of days in each month as well as leap years. This generally means that the watch will not need to be reset for more than a century assuming the movement keeps running.
Water Resistance - Water Resistance indicates how well a watch is sealed against the ingress of water. It is usually indicated by a static test pressure that a sample of newly manufactured watches is exposed to in a leakage test. The test pressure is commonly indicated as a water depth in meters.
Most watches are water resistant, meaning that they resist but are not impenetrable by water. Water resistance is not a permanent condition. For example, the gaskets around the stem, case back and glass deteriorate over time. If the case, glass or seal is damaged in any way the watch is no longer water resistant. For this reason, water resistant watches used for swimming activities should be serviced from time to time.
Retrograde - In the context of a watch it indicates that the pointer hand does not make a full revolution through a circle on a sub dial but rather moves incrementally along a scale and then jumps back to the start.