Definition of "foo"

noun:
- A metasyntactic variable used to represent an unspecified entity. If part of a series of such entities, it is often the first in the series, and followed immediately by bar.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
- Fool, foolish person.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License
interjection:
- Expression of disappointment or disgust.
  
  from Wiktionary, Creative Commons Attribution/Share-Alike License