For those of you don’t speak e-book techno babble, DRM stands for “digital rights management“, which is an obfuscated way of saying that an e-book (or other electronic media) has encoding which limits on what device it can be used. In the Amazon Kindle world, this means that any DRM-encoded e-book you buy from Amazon can only be read on your Kindle devices or apps. You may be able to virtually loan it a limited number of times if that feature is enabled, but you cannot simply take the file and copy it to any device you own and read it there, instead.
While it is easy to see why publishers are tempted to use DRM in order to try to limit piracy while perhaps also increasing sales by forcing people to buy instead of borrow e-books, there are many who feel this policy is counter-productive and may actually encourage piracy in some cases. (Yours truly does not claim to know which viewpoint is correct, nor am I sure there is enough empirical data out there to decide.) The up side for us readers is that DRM-free e-books become a bit more like their paper ancestors, in that the e-book files we purchase become ours to do with as we like: read on any device we choose, lend to friends to read, give to someone else when we’re done with it. However, I think the most important thing to me is that such files, by not being locked to a specific device I own, mean that I now can own the book for life regardless of whether or not the device for which I originally purchased it remains a viable platform.
There is a certain logic in a speculative fiction publisher being on the forefront of such a technological experiment. I hope their speculation that going DRM-free will enhance their public relations — and thus their business — will bear fruit.