Samsung has filed a patent with the World Intellectual Property Organization (WIPO) outlining a design for multiple displays on a single handset in four different iterations. For each style of device, displays are found in the usual front position, as well as on at least one edge and the rear panel. Based on the design sketches themselves and subsequent descriptions, all of those seems to utilize flexible panel technology but none appear to be of the folding variety which has cropped up quite a bit over the past few months. However, that doesn't mean this display configuration wouldn't be useful. Each of the displays appears to be active with touch and gestures enabled. That means multiple apps could be used at once with just the flip of a phone instead of having to enter a multi-window mode or swap back and forth between apps. Meanwhile, the edge might be used for notifications or similarly important information or controls.
Moreover, the use of an edge-mounted display isn't altogether surprising either since Samsung has already incorporated something that looks very similar to at least one design in the 'Edge' variations of its flagship handsets. Having the full edge to work with might inspire new software improvements and functionality too, such as an edge based in-display fingerprint scanner or volume and brightness controls. That's especially true with regard to the kinds of aftermarket software typically created by the larger developer community. The primary difference, in the meantime, is in the use of a rear display. That could feasibly allow for a much higher screen-to-body ratio since the main camera might be used as a selfie-shooter as well, although that's hardly the only use that could be found for it.
Whether or not Samsung will ultimately use any of the designs in the patent is entirely up in the air at this point. Given the rumors and leaks regarding both the Samsung Galaxy X and the Samsung Galaxy Note 9, there's little chance any of the designs might be incorporated there. At very least, any implementation of this patent seems to be quite a ways off, if it's ever used at all.