Fedora Core and later Fedora !
Ubuntu is a computer operating system based on Debian Linux and is freely distributed. Ubuntu wiki is a site which answers questions on this software.
Yes. BackTrack is a Linux distribution that focuses on penetration testing and computer forensics.
No, Ubuntu is part of Linux.
Yes.
This is difficult to determine. Judging solely from server hardware sales, Linux has only about 30% of the market. However, most high level sites run Linux, and it seems likely that Linux has a much higher market share than is indicated. More importantly, since the majority of Linux distributions are available freely, a large portion of Linux servers are not accounted for in many market share statistics because these stastics are approximated based on license sales. Therefore the very large number of Linux servers that are running on freely distributed licenses are not included in these calculations.
Linux is distributed as Red Hat
Ubuntu is a Linux distribution (as in a specific OS setup with the Linux kernel.)
Yes.
Scientific Linux is a Linux distribution. It is a free and open source operating system and aims to be as close to the commercial enterprise distribution as possible.
Distributions
Freely distributable Unix/Linux systems come with the source code, which can be modified. Proprietary Unix systems are distributed as binary only, with no source code, so you can't modify the system (easily). Other reasons are legal: the proprietary systems are copyrighted, and the freely distributable versions should not have any copywritten code in them, thus allowing them to be distributed without licensing arrangements.
The short answer is that Linux is a computer operating system, and is an alternative to older products such as DOS, Windows, MacOS or UNIX. The way that Linux is written and distributed is new and revolutionary - it is maintained by an open community of programmers and you can get it for free. This has created a growing industry of distributors who bundle Linux and other useful stuff into a distribution package or distro, to make life easy for the end user. This method of development and distribution is protected by an equally revolutionary license, the GNU Public License