Game world border
Player can reach the border of the game world, usually an inexplicable, impenetrable and invisible wall of nothing. Often with blackness on the other side though not necessarily.
The first video game about Game world border was released on March 20, 2006.
This can be explained in-mythos as "operation zone" or similar.
Top-down strategy games should not be included as the existence of borders is so prevalent in them (and usually only gone based on genre, such as in 4X and grand strategy).