Linux vs Linux Distributions
What is the difference between Linux and Linux distribution?
Linux is the core of the operating system i.e. the kernel. Kernel manages the physical resources of the computer and performs tasks such as starting and stopping programs, allocating memory, managing the processor, and managing network connections.
A Linux distribution contains the Linux kernel along with entire suite of Linux software such as GUI, editors, networking tools, administration tools, and pretty much everything you would see or use. The Linux distribution makes Linux useful and user-friendly. Different Linux distributions have different set of software and configurations. Most commonly used distributions of Linux are Red Hat Enterprise Linux, Fedora, SUSE, and Ubuntu.
What is the difference between different Linux Distributions? The valued-added tools that are packaged with each distribution.
Which distribution is better or the best? The answer depends on your needs. Do you need commercial support? Are you going to be using Linux for server or desktop? Which packaging system do you prefer? Which distribution is more suited for your line of work? It all depends on the answers to these and many other questions.
If you are learning Linux, start with Ubuntu or Fedora since they are commonly used and you would get plenty of support from the user-community.
Also see http://en.wikipedia.org/wiki/Comparison_of_Linux_distributions for a more comprehensive comparison of the differences.