Demilitarization is the act of taking weapons and soldiers out of a country or an area, so that fighting cannot easily start there. You meet it in the news and in peace talks, not in daily chat. A demilitarized zone is a strip of land where neither side is supposed to keep an army — the line between North and South Korea is the famous one. Though actually, people sometimes use the word a little widely, and say a place has been demilitarized even when a few guards remain. The tidy meaning is still: no army, no heavy weapons, no fighting from that ground. This word is about a PLACE. Sending soldiers home is a different word: demobilization.