The ground between trenches where a soldier from either side would be easily targeted
No man's land is a term for land that is not occupied or more specifically land that is under dispute between parties that will not occupy it because of fear or uncertainty. During war (especially World War I), it is a term used as the area of land between two enemy trenches that neither side wishes to openly move on or take control of due to fear of being attacked by the enemy in the process. It is also a term for the stretch of land between two border posts, when one exits one country at their border post and when one enters the next country at their border post, usually just a few metres away, though at some (usually remote) border crossings it can be measured in kilometres
an unoccupied area between the front lines of opposing armies land that is unowned and uninhabited (and usually undesirable)