one fatally pierced; a person run through and killed or left dying, above all the battlefield dead
This is overwhelmingly a word of war. A חָלָל is a body that has been pierced through by sword, spear, or arrow and so brought down. It pictures the result of violence on the field: corpses strewn over the ground, the heaps of the dead after a defeat, the fallen of a nation.
The word reaches from the moment of the wound to the still corpse. Most often it names those already dead, the slain who lie unburied or are counted after the fighting. But the same word also catches the one freshly run through who has not yet died, the mortally wounded man still groaning before he falls silent. Hebrew does not separate these with two words: the man pierced to death is a חָלָל whether he is dying or dead.
Because it is so closely tied to bloodshed, the word carries a heavy weight of horror and judgment. Prophets pile it up to describe the dead of Egypt, Tyre, and Edom going down to the grave, and the law treats the unexplained חָלָל found in a field as a stain of guilt on the land until it is dealt with.