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