Each time the medium to be printed passes throug the machine is a pass. Simple printing presses require mulitple passes for various colours or two-sided printing; sophisticated presses can print all colours (and even both sides) in a single pass.

sample refs:

Speedmaster SM 102 drupa 2004 Generation

Das beidseitige Drucken in einem Durchgang bei höchster Druckqualität zeigt das einzigartige Potenzial der Speedmaster SM 102. Ausgestattet mit den Plus-Optionen erlaubt die Speedmaster SM 102 dem Drucker ein zukunfts- orientiertes Arbeiten.
http://www.heidelberg.com/www/html/de/content/products/sheet...

Speedmaster SM 102 drupa 2004 Generation

Double-sided printing in a single pass with highest print quality illustrates the unique potential of the Speedmaster SM 102. Equipped with the "Plus" options, the Speedmaster SM 102 enables printers to work with an eye on future developments.

Widerdruck
Der zweite Druckgang, bei dem die Rückseite des Druckbogens bedruckt wird, heißt Widerdruck. Den ersten Durchgang bezeichnet man als Schöndruck.
http://www.heidelberg.com/www/html/de/glossary/glossaryitems...

Schön- und Widerdruckmaschine
Bogendruckmaschine, die den Druckbogen in einem Bogendurchlauf beidseitig (Schön- und Widerdruckseite) bedruckt.
http://www.heidelberg.com/www/html/en/content/products/sheet...
http://www.heidelberg.com/www/html/de/glossary/glossaryitems...

Perfecting machine
Usually a sheetfed press that prints on both sides of the paper in a single run.
http://www.heidelberg.com/www/html/en/glossary/glossaryitems...

Perfecting: Printing both sides of the paper (or other material) on the same pass through the printing machine.

Perfecting Press: A printing press that prints on both sides of the page in a single pass.
http://www.sandyinc.com/resources/glossary.html?db_item=glos...

Special Colours

This refers to colours which are produced using specially mixed inks from one of the commercially available colour ranges such as Pantone, DIC or Focoltone. They are most commonly used when using Two Colour Printing.

To print colours outside the range of four colour process it is necessary to use special inks. If for example the exact colour of a company logo could not be achieved from a CMYK mix then it would be necessary to print a fifth plate with the special ink. It is not unusual, where an elaborate effect is required, to print in six or more colours. There are presses which are capable of printing eight different plates in a single run through the machine.

Two Colour Machine

A press which prints two colours during one pass through the machine. It is possible to print four colour process by printing Cyan and Magenta, changing the plates and then sending the sheets through again to print the Yellow and Black.

The word 'run' is also apparently used sometimes, but I'd be wary of that, since 'press run' or 'print run' is commonly used to refer to all the items printed in a single job (regardless of the number of passes through the machine)

http://www.bobs.co.uk/print/glossary.html