GSM

Refers to the weight of the paper in grams per square meter. Note that the weight in pounds is not the weight per square foot, but the weight of 500 of some arbitrary size sheet (for copy paper it is for a 17x22" sheet - for book paper it is 25x38". ). 20# copy paper or 50# book paper is about 75 gsm.

Paper Stock

This refers to the type of paper you want to print onto, recycled, bond stock, card stock, etc…

Finish

This refers to the look and feel of the product once printed – will it have a matt finish, a gloss finish or a silk finish.

Bleed

“Bleed”is a printing term that refers to printing that goes beyond the edge of the sheet after trimming. The bleed is the part on the side of your document that gives the printer that small amount of space to move around paper and design inconsistencies.

Crop marks

These help the printer to check whether the printing plates are lined up. If you see these marks on your proof they will not be printed – they are a guide for the printer and will be guillotined off.

Print Ready

This refers to a file that is ready to submit to a printer, it means it will have all of the registration marks (crop marks), accurate Bleed, fonts converted to outlines (if required for the format) and it will be ready to place on the press.

DPI

DPI stands for Dots per Inch. It is a measure of resolution for page printers, photo type setting machines and graphics screens. This is an important specification before doing any kind of printing. Most printers require files set to 300 dpi and over. Generally 72dpi are files that are good enough for web and email but not for print

High Resolution

This just means that the file provided must be 300DPI and over. Any file over 300DPI is considered as High Resolution. It just means that the quality of image and graphic will be of the highest quality and will not appear pixilated when printed.

Pixels

A pixel is generally thought of as the smallest single component of a digital image. The more pixels used to represent an image, the closer the result can resemble the original. The number of pixels in an image is sometimes called the resolution, though resolution has a more specific definition

Offset printing

Offset - Compared to other printing methods, offset printing is best suited for cost-effectively producing large volumes of high quality prints in an economically sound manner that requires little maintenance

Offset lithography is one of the most common ways of creating printed matter. A few of its common applications include: newspapers, magazines, brochures, stationery, and books.

Many modern offset presses use computer to plate systems as opposed to the older computer to film work flows, which further increases their quality.

Advantages of offset printing compared to other printing methods include:

• Consistent high image quality. Offset printing produces sharp and clean images and type more easily than letterpress printing because the rubber blanket conforms to the texture of the printing surface.
• Quick and easy production of printing plates.
• Longer printing plate life than on direct litho presses because there is no direct contact between the plate and the printing surface. Properly developed plates running in conjunction with optimized inks and fountain solution may exceed run lengths of a million impressions.
• Cost. Offset printing is the cheapest method to produce high quality printing in commercial printing quantities.

Digital printing

Digital printing is a method of printing using digital techniques in which the data and images are printed directly from a computer onto paper, including those developed for computer printers such as inkjet or laser printers.

• Every print can be different, because printing plates are not required, as in traditional methods.
• There is less waste chemical and paper, because there is no need to bring the image "up to colour" and check for registration and position.
• The ink or toner does not permeate the substrate, as does conventional ink, but forms a thin layer on the surface and may in some systems be additionally adhered to the substrate by using a fuser fluid with heat process (toner) or UV curing process (ink).

Because there is less initial setup, it is useful for rapid proto-typing, and cost effective for small print runs.

With Thanks to Wikipedia for supplying most of this information