There are some of the basics (if anybody knows of others, please PM me and I'll add them)
All Rights: If you offer a publisher all rights, then they will own the article or manuscript. If they accept it and then you wish to publish it elsewhere, then you will need to get permission from the publisher first.
First Rights: If you offer a publisher first rights, you are promising that this will be the first time the article has been seen in public anywhere.
Second, Third, Ect, Rights: Second rights tell the publisher that is has been published once before, ect. You will need to tell the publisher when and where it previously appeared.
Regional Rights (i.e. First American Rights, First Australian Rights): A regional right promises that it is the first time the article has appeared in that particular region. You could offer one publisher First North American Rights, and another publisher First Australian Rights.
First Electronic Rights: This is the first time it has appeared on the internet.
Here is a helpful link that was passed on to me to share with everyone
http://www.writing-world.com/rights/copyright.shtml
Amy thought I should add this to her info on rights:
You can post your Challenge Entries anywhere you want AFTER the winners are announced for that week, to avoid any chance of the judges seeing it by accident before all the scores are sent to FW.