Foo: A metasyntactic variable used in computer science as a placeholder term or to represent any abstract concept. By extension, a placeholder for any as-yet-unnamed product, company, or process: "We'll create the Foo umbrella brand, and then develop a family of brand extensions--Foo-X, Foo-Y, Foo-Z."
Foo Camp is an annual invitation-only "weekend geek campout" hosted by O'Reilly Media, where "people who're doing interesting works in fields such as web services, data visualization and search, open source programming, computer security, hardware hacking, GPS, alternative energy, and all manner of emerging technologies to share their works-in-progress, show off the latest tech toys and hardware hacks, and tackle challenging problems together." In this usage, "Foo" also stands for "Friends of O'Reilly."
At the 2007 Foo Camp, held in June at the O'Reilly campus in Sebastopol, California, lexicographer Erin McKean led participants in a word-making session she called--in deference to her techy audience--"hacking English." Among the coinages (more complete list here) were Googlegänger ("the other person who shows up in Google search results when people search for you"), malignation ("the state of being maligned"), and jot ("joyously hot").
For a comprehensive survey of foo etymology, history, and usage, see this 2001 paper from the Network Working Group.