For both developers working on HTC devices and the end users wishing to get the most from them, achieving S-OFF is one of the major stumbling blocks that stands in the way of a fully customizable device. To sum it up as simply as possible, the S stands for security and achieving S-OFF is the process of unlocking the devices NAND storage. S-OFF is usually achieved sooner or later for the majority of HTCs devices. However, sometimes it can take a while to get there. One of the most recent devices to join this club is the HTC Jetstream, thanks to the rather bizarrely named Juopunutbear utility.
XDA Recognised Developer Fuses posted news of the Jetstream becoming a supported device for this tool earlier in the week, and it now sits alongside other popular HTC devices such as the Amaze, Sensation and Evo 3D (CDMA/GSM) among others. While the process is pretty simple on paper, something like this always has the potential to go wrong. Make sure you read up and understand the risks/potential problems before attempting this yourself. You will also need to have your bootloader unlocked via HTC Dev before trying this out.
Take a look at the original development thread for more details, as well as a link to find out exactly how to pronounce “Juopunutbear.”