Linux Kernel

• Linux is a family of operating systems all built on the same kernel -- the set of core functions for communication between a computer's hardware devices and the programs running on it. Unlike many other operating system kernels, Linux is open-source -- its entire source code is freely distributed and available for modification. Because of this, there are many different versions, or "distributions," of Linux, designed and distributed by many different groups.
  
  

Ubuntu

• Ubuntu is a distribution of Linux maintained by Canonical Ltd. Though Canonical is a private company and Ubuntu is its primary product, Ubuntu is still an open-source Linux distribution and available for free download. Because of its ease of installation and reputation for stability, Ubuntu is often installed on computers that act as servers, although many people also use Ubuntu as their primary operating system even for casual use.
  
  

Ubuntu Versions

• Canonical releases a new version of Ubuntu every six months. Versions are numbered according to their date of release: thus, the current version as of this writing, version 11.04, was released in April 2011. In addition to their numbers, versions have alliterative animal names: 11.04, for example, is also called Natty Narwhal.
  
  

Dapper and Edgy

• Dapper and Edgy are the short names for Dapper Drake and Edgy Eft -- Ubuntu releases 6.06 and 6.10, respectively. Dapper Drake is a Long-Term Service release -- technical support and Canonical updates for it continued for five years, while Edgy Eft's lasted only 18 months. Though both of these Ubuntu versions have been replaced many times over, you may still come across servers running Dapper Drake.