The Hyperfocal Distance sounds like a geeky photography term. That’s because it is, but the idea is both simple and useful.
In general, when you focus on a person or object there will be other objects, both closer and further away, which are also in focus because they fall between the near and far distances which define the “depth of field”. Anything closer than the near limit of the depth of field, or beyond the far limit, will be out of focus. The further away the object you are focusing on, the wider the depth of field. Eventually, as you keep increasing the focusing distance, you hit the point (known as the Hyperfocal Distance) where the far limit of the depth of field just coincides with infinity. That means everything between the near limit and infinity will be in focus. For any given lens, focal length and aperture, this is the widest depth of field you can get, and very useful if you just want to get as much as possible, including the background, in focus.
It is so useful that there are countless websites and iPhone apps etc to help you calculate it. Which is fine, except you have to read off the focal length of your lens as best you can (if it is a zoom), check then enter the aperture, run the application to get the Hyperfocal Distance then focus to that distance manually, as best you can within the limits of the rather sparse focus distance scale (if any) on your lens. The result may be roughly right but it is fiddly and rather hit and miss. You would do as well to focus manually with your depth of field preview button (if any) depressed until the background looks like it is just in focus. Not very scientific but gets you somewhere near the result.
How much better, though, if DSLRs had a button which set the focus to the hyperfocal distance automatically for you, in an instant. It would make most sense if you were in Aperture Priority mode, but it could be useful with any mode.
Hardly difficult for the manufacturers to offer this. The camera’s electronics already have access to all the data they need.