The near focus is simply the closest distance you can focus a telescope. It’s good to know when using the scope for terrestrial visual or photographic purposes.
Different types of telescopes will have greatly differing near focus capabilities. In general, catadioptric designs, like Maksutovs (MAKs) and Schmidt-Cassegrain telescopes (SCTs), are superior, with small near focus distances. Refractors and Newtonian reflectors will have much larger near focus distances and may not focus closer than several hundred feet (50 to 100 meters).
Most of Celestron's iconic SCTs can focus as close as 20 feet (6 meters). Older models of the C-90 MAK can focus as close as 6 feet (2 meters).