An alternative operating system to that of windows or mac. Can be used for servers, mobile phones and digital tv recievers. Can be customised to suit the user. Is based on Unix, Written by Linus Torvalds.
There are about a hundred different versions of linux distributed to millions of people on billions of computers-so you can bet your ass that one os will be different from the next. Linux allows the user to re-program the software to suit them-this is how many software glitches are sorted out with one person programming one part of the system while another person focusses on another part. Windows only allows this to an extent (ie changing a user name or startup sounds or desktop background etc) so for this reason many software bugs cannot be fixed and hence windows being so unstable. Linux is good for driving mobile phones or powering servers but is impractical for use with the average computer gamer/secretary/photo editor. In other words, a person with programming experience would opt for Linux as they can customise it to suit them, whereas a person wishing to read email or surf net would opt for Windows or Mac as they will not have to know anything about programming first.
Newer versions of linux can make applications (ie Windows media player or Mac video editor) run with Linux.
Note: A particularly bad combination is: Dell computer, Pentium 4 CPU and Windows XP. Try switching the combination (ie fit an AMD Athlon CPU)-this i am pointing out as many unstabilities are rooted to the CPU and combination of hardware components, rather than the actual software itself.