Pantone PMS is actually an acronym for the Pantone Matching System.
Today's Pantone Matching System features 1,341 Pantone solid colors, printed on coated adn uncoated papers. Each page contains 7 colors, with ink mixing formulas. The pages also include an RGB icon , indicating colors achievable on-screen, and an CMYK icon , indicating colors achievable in CMYK color printing. Colors that bear both the RGB and CMYK icons are ideal choices for designs that will be reproduced using multiple processes.
With the Pantone Matching System, you get maximum color consistency from designer-to printer-to ink maker-to client. It is the real strength of the Pantone Matching System. If everyone in the process has a Pantone formula guide, they can look at the same 185 red, and they are all seeing the same color. The designer specifies a color, the printer orders ink in that color, prints using that color, and the client gets exactly what they want. This end to end color control explains why Pantone has become the worldwide standard for color since it's introduction.
Software developers have also made it easy for designers to incorporate Pantone solid colors in their design projects. There are some issues, however. The Pantone formula guides are printed using inks and pigments, while computer monitors reproduce the colors using Red Green and Blue light. This issue causes a lot of confusion due to the different appearance of printed Pantone colors and viewed Pantone colors (on a computer monitor). That's why it advisable to only use a Pantone formula guide to specifiy or determine a Pantone solid color.
More information on Pantone solid formula guides here.