A Linux Distribution (distro) is lika a flavour.
For example:
You can go to a dairy bar and ask for ice cream, but you need to specify which kind of ice cream. Chocolate ice cream, strawberry, bubble gum, etc...
You can run Linux, but you need to pick a specific type of Linux such as Ubuntu, OpenSuse, Fedora Core, Gentoo, Debian, Slackware, etc..
Different distros are generally suited for different things.
There are desktop distros like Ubuntu and Mint, that are focused on end users and doing your day to day stuff like browsing the internet, writing a report for work or school or MSNing your friends.
Some Linux distros are meant for running servers. These would be things like RedHat, Debian and Slackware. These will run your company website or an email server.
Yes. BackTrack is a Linux distribution that focuses on penetration testing and computer forensics.
No, Ubuntu is part of Linux.
Yes.
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.
No Linux distribution is currently made for any PalmPilot model.
Many Linux distributions are intended for home users.
A server with a Linux distribution installed on it.
Linux Security Tool Distribution (STD) is really good.
SUSE Enterprise Linux. They also contribute heavily to OpenSUSE.
Linux Distribution