1. A layout for antenna towers in a wireless network that allows a large number of towers to cover a large contiguous area and serve a large number of simultaneous users. Each antenna tower provides coverage for a certain area, and coverage of neighboring towers overlaps, so that coverage is seamless for users. Two such neighboring towers user different radio frequencies so that they don't interfere.
However, imagine that tower A overlaps with tower B, and B overlaps with tower C. But A and C do not overlap. In that scenario, A and C might use the same radio frequency, since they would not interfere.
2. A radio frequency band near 850 MHz.
See: Band 5