Glossary of Terms
 
  extension  
  The term that Apple Computer, Inc. uses for drivers and other functions on Macintosh computers. Extensions are found in the Extensions folder, which is located in the System folder on a Macintosh. Some examples of extensions are Finder Help, Foreign File Access, and QuickTime.  
  Source: Yamaha  

Related terms:
  CBX driver   Host Select switch   Mac   PC   To Host port   driver   serial port driver