a raised signal: a pole, standard, or banner lifted up high so everyone can see it and respond
At its core this word names something set up high to be seen from far off. It is not a decoration but a working signal: a pole, staff, or standard raised on a hill or held aloft so that people gather, march, take warning, or take courage.
Most often it is the rallying standard of war and summons. Prophets picture God raising one on a bare mountain to call distant nations to muster, to gather scattered Israel home, or to signal an attack on a city. The point is always visibility and response: the signal goes up, and those who see it move.
The same idea stretches naturally to other raised objects. In the wilderness Moses mounts the bronze serpent on such a pole so the whole camp can look and live. Korah's censers, hammered into a plating for the altar, are left standing as a permanent visible warning. And a ship's sail, the great sheet hoisted up the mast, is named by the same word. Whether it summons, warns, or catches the wind, it is the thing lifted up for all to see.
The famous altar name "The LORD is my Banner" (Yahweh-Nissi) draws on the rallying sense: God himself is the standard his people rally to and fight under.