Automatic Watch An automatic watch requires no battery. The watch mainspring is wound automatically by a balance wheel which rotates due to normal wrist motion whilst wearing the watch.  There are 2 types of automatic watches i.e. mechanical and automatic.  Mechanical watches have to be wound up and automatic watches work on the movement of the wrist.
Bezel This is the ring around the case which holds the crystal of a watch to the case of the watch.  
Bi-Directional Rotating Bezel  A bezel that can be rotated either clockwise or anticlockwise. 
Buckle The traditional loop and pin buckle is called a 'buckle'. A hinged fold-over style metal clasp that opens and closes easily, allowing the watch to be placed on the wrist.
Calendar A feature that shows the date, and often the day of the week and month. Most calendar watches show the information digitally through an aperture on the watch face.  If watches have perpetual calendars this will mean that the date will automatically change at the end of the month.  Some  chronograph watches show the information on sub-dials on the watch face. 
Calibre The mechanism inside the watch that tells the quality of the watch movement.
Case A case of a watch is the primary housing for the internal watch movement.
Case back The bottom of the watch case that can be opened for access to the watch movement for repair or battery change.  Some watches have a sapphire glass backing which allows you to see the working mechanism of the watch.  
Chronograph This is a watch with a variety of extra features displayed on sub-dials.  This can include hours, minutes, seconds, power reserve, date and moon phase.
Chronometer This is a watch which has been measured for accuracy and tested for precision by an official testing institute.
Complication An additional function other than basic timekeeping of the hours, minutes, and seconds. Certain features such as automatic winding or date are considered complications. The main complications are power reserve, moon phase, GMT, and full calendars. Great complications are split second chronographs, perpetual calendars, tourbillons, and minute repeaters.
COSC This is the Swiss Official Chronometer Testing Institute that will certify the official chronometer status of a watch.
Crown The 'Crown' is known better as the adjustment dial on the watch. The crown is used to adjust the time, date and for winding up the watch. 
Crystal The 'crystal' is the  transparent cover over the dial. The crystals can either be made from resin, minerals or sapphires. 
Date Window A small opening in the dial through which the date is displayed.
Deployment Buckle The deployment buckle is a clasp that folds nicely in to the strap for elegancy.
Dial The 'dial' is the face of the watch showing the time. 
Diving Watch A watch that is at least 200M water resistant. Has a one way rotating bezel and a screw-on crown and back. Some watches have a helium escape button to release the pressure after the diving
Escapement Set of parts (escape wheel, lever, roller) which converts the rotary motion of the train into to-and-fro motion (the balance).
End of Battery Life Indicator (EOL) The EOL indicates when it is time to replace the existing battery. Different manufacturers use different methods to indicate a low battery, i.e. if a second hand usually sweeps, when the battery is low it will begin to tick.
Finishing The finishing of watches come in three types of finishing's, a polished surface, a brushed finish and a gold plated finish.
Fly-Back Hand (Retrograde Date Hand) Usually, a hand indicating a date or time against a scale and then 'flies back' to catch up with to another date or time. For example, a hand that 'flies back' to the beginning of the month after reaching the 28th, 29th, 30th, or 31st day of the month.
Geneva Stripes A form of decoration in higher grade watch movements which look like a pattern on the face of the watch. 
Grand Complication A Grand Complication is a combination of complications but it must have a perpetual calendar with or without moonphase indication), a split-second flyback chronograph and a minute repeater. Manufactures quite often include many other complications as well. 
Horological The art of making a Timepiece.
Jewel In watch making, a synthetic ruby used for making low friction bearing in which the delicate pivots of the movement wheels run in. In some deluxe watches, sometimes sapphires or garnets are used. Expensive watch movements are jeweled from the barrel to the balance, and all automatic work, date and complication movements are expected to be jeweled.
Luminous The hour markers and/or hands have a feature coating of a glow in the dark which will illuminates in the dark so you can tell the time where there is insufficient light.
Manufacture A French term for a watch factory which itself produces the components needed for the manufacture of watches.
Mechanical Automatic Wind A watch which has mechanical moving parts and winds its mainspring automatically using an internal rotor system.
Mechanical Manual Wind A watch which has mechanical moving parts and requires its mainspring to be manually wound.
Moon-Phase Calendar On some watches, the display of the evolution of the lunar cycle: rising, full or waning moon.
Movement This is the internal mechanism of a watch. Assembly of parts and main components such as the mainspring, balance assembly, escapement, train of wheels, setting and winding .
Perpetual Calendar A complication or function of a watch which displays correctly without adjustment, the day, date and month, and can also account for leap year cycles.
Power Reserve Indicator A 'Power Reserve Indicator' shows the power resource of a mechanical movement watch.
PVD (Physical Vapour Deposition) A method of coating thin watch cases by integrating titanium particles and then depositing gold for color. (Usually comes in black finish)
Quartz This is a  watch with a battery-powered mechanism.
Retrograde This is a pointer hand on a watch dial which returns to zero at the end of a prescribed period i.e. days/months. For example a watch may have a retrograde date,  meaning that the hand moves up a scale a day at a time, pointing to the current date, when it reaches 31 it will spring back to 1.
Rotor In automatic winding mechanisms, an unbalanced, semicircular metal turns freely in both directions winding the mainspring.
Sapphire Crystal A Sapphire Crystal is a synthetic watch crystal that is extremely hard and very scratch resistant.
Skeleton Movement Movement on a watch where the plates have been removed or trimmed so that you can see the gears and other parts. 
Skeleton Watch Crystal on the front and back. 
Waterproof No watch can be 100% waterproof.
Water Resistant Describes a watch case designed to prevent water from entering.
Tachometer (Tachymeter) A watch or stop watch used for the measurement of speed.  It measures speed in kilometers per hour based on 1000m distance.
Tourbillon This type of watch is a complex piece of micro-engineering which results in the escapement of a watch rotating on its own axis; the aim is to cancel out the variations in running regularity which can be caused by the watch being in different positions; (a watch may gain in one position yet lose in another).