The near focus is simply the closest distance you can focus a telescope. It’s a good number to know when using your scope for terrestrial visual or photographic purposes.
Different types of telescopes will have greatly differing near focus capabilities. In general, catadioptric designs like SCTs and Maks 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 (50-100 m).
Most of Celestron's iconic SCTs can focus as close as 20 ft (6 m). Older models of the C-90 MAK can focus as close as 6 ft (2 m).