The patent, which can be found in scanned form on the US Patent and Trademark Office, outlines a "method and device for illustrating a virtual object in a real environment". Yes, that's a somewhat vague description, though it's made up for by an overly elaborate summary:
The invention relates to a method for representing a virtual object in a real environment, having the following steps: generating a two-dimensional image of a real environment by means of a recording device, ascertaining a position of the recording device relative to at least one component of the real environment, segmenting at least one area of the real environment unmarked in reality in the two-dimensional image for identifying at least one segment of the real environment in distinction to a remaining part of the real environment while supplying corresponding segmentation data, and merging the virtual object with the two-dimensional image of the real environment with consideration of segmentation data such that at least one part of the segment of the real environment is removed from the image of the real environment.
To put it simply, the patent describes using augmented reality to replace or add objects to a real scene. The lead image of this story, taken from the patent documents, makes it pretty clear how this would work in practise.
There's also this adorable sketch:
The patent is light on specific implementation plans and is broad enough to cover a large swathe of uses for augmented reality, so it's impossible to know how Apple might utilise the patent.
That said, you could read a lot into the patent's focus on furniture -- some sort of interactive interior decoration app, perhaps?