The opening in the Earth's surface through which lava can flow is called a vent.

Here are some related terms:

* Volcano: A mountain or hill, typically conical, having a crater or vent through which lava, rock fragments, hot vapor, and gas are erupted from the Earth's crust.

* Crater: A bowl-shaped depression at the summit of a volcano, formed by the eruption of lava, rock, and ash.

* Fissure: A long, narrow crack in the Earth's crust through which lava can erupt.

So, while a vent is the specific opening, it's usually part of a larger volcanic structure.