In a move that Novell says is designed to make its intentions clear when it comes to any patents it may have to the open source software (OSS) it distributes, Novell has issued a policy statement saying that those patents are purely for defensive purposes. Patents on software is a controversial issue these days because of how they basically result in government-sanctioned monopolies. If a patented technology become a defacto standard, the patent holders can use that patent to extract royalty payments from vendors and users that rely on the technology. Such "extortion" falls into the realm of offensive patents.
Defensive use of patents on the other hand is a technique that companies use to protect themselves from patent infringement lawsuits. If I have a patent on a technology, you theoretically can't sue me for patent infringement. By declaring its defensive intentions, Novell is trying to convey the message that its patents help protect the licensees of open source software from being sued for patent infringement the way Microsoft might be able to sue licensees of the open source-based OpenOffice. While patents may offer such protection to OSS licensees, OSS advocates don't necessarily agree that patents on software are a good idea. The Free Software Foundation's Richard Stallman, for example, remains a vocal opponent to the idea of patents on software.