Hyperfocal distance is the focus distance that gives the maximum possible depth of field for a given focal length and aperture, with everything from half that distance out to infinity landing acceptably sharp.
Hyperfocal focusing is how landscape photographers get a flower a foot away and a mountain on the horizon both acceptably sharp in one frame, without stopping down so far that diffraction softens everything. Focus on the flower and infinity goes soft; focus on infinity and the foreground goes soft; focus at the hyperfocal distance and the sharp zone runs from half that distance all the way out. Getting it wrong wastes the trip.
Autofocus locked onto a bright horizon can leave the near rocks visibly mushy in a print, and sharpening in editing will not put real detail back. The distance is not fixed, either. It moves with focal length and aperture, so a 16mm frame at f/8 and a 35mm frame at f/8 need very different focus points, which is why photographers check a table or a calculator instead of guessing a third of the way into the scene.
Shooting a coastal scene on full frame at 20mm and f/11, the hyperfocal distance works out to about 1.2 metres. Focus there and everything from roughly 0.6 metres to infinity records as sharp, covering a tide pool just in front of the tripod and the cliffs across the bay. Change to 35mm at the same f/11 and the hyperfocal distance jumps to about 3.6 metres, so focusing at 1.2 metres now leaves the far cliffs slightly soft.
Stopping down to f/16 at 20mm pulls the hyperfocal distance in to about 0.85 metres and buys a little more foreground, but past f/16 diffraction costs more sharpness across the whole frame than the nearer focus point gains. In practice many photographers focus a touch beyond the calculated distance as a safety margin for infinity.