Significant portion of player's work is spent exploring areas, examining areas, searching for where various things can be found so they can be later exploited, etc. Best examples of this are when there's no objective markers and player can get lost.
The first video game about Exploration was released in 1978.
* Open areas (open world or just man paths to take that don't all lead to objective)
* No objective indicator or other clear instructions where to go
* No map
This should NOT be used if the purpose of the exploration has a specific purpose that has a better tag (e.g. prospecting) or is for very specific purpose (e.g. finding where the enemy base is in wargames).
But for example if this is required to find anything to actually do to progress, then it's better suited here.