It is the minimum distance an object must be for it to be brought into focus.
A spotting scope is a small telescope that has been modified for use by day. A spotting scope differs from an astronomical telescope in several important ways.
First, a spotting scope always produces an upright image whereas a telescope used in astronomy may produce a reversed image or even an upside down image (not a problem for astronomy).
Second, a spotting scope is much smaller in size than an astronomical telescope, mainly for the sake of portability.
Third, a spotting scope is a lower magnification instrument than a telescope, since the atmosphere by day does not allow the high magnifications used in astronomy.
Fourth, a spotting scope is mounted on an ordinary photo tripod, but a telescope for astronomy requires a very specialized mount, often unsuitable for daytime use.
Lastly, many, if not most, spotting scopes are waterproof and fogproof - a rare feature in an astronomical telescope.
Since the prisms in the binocular overlaps closely, the objective lens and the oculars lens are aligned, the binoculars will be slimmer, more streamlined, less bulky and more rugged than a Porro-Prism binocular.