SRD = System Resource Document. http://www.wizards.com/default.asp?x=d20/article/srd35
Basically anything in there is fair game to use in your own products. Anything else published by Wizards of the Coast (with the exception of a few things in Unearthed Arcana) cannot be touched by any 3rd party publisher.
Basically anything in there is fair game to use in your own products. Anything else published by Wizards of the Coast (with the exception of a few things in Unearthed Arcana) cannot be touched by any 3rd party publisher.