What is the passage in a volcano that magma flows to the surface through called?

The Pipe.

Magma chamber underneath, then the pipe and finally the crater for the lava to flow from.

I'd heard it was a chimney, Teach. Seems someone else thinks so, too.
http://news.softpedia.com/news/How-Do-Volcanoes-Work-69925.shtml

"This primary magma is hotter and lighter than the surrounding material, ascending to the surface and stops into a point called magma chimney, a gathering location of the network of tunnels through which it has advanced till then."

Correct term is vent.

Vent: The opening at the earth's surface through which volcanic materials issue forth

Pipe: A vertical conduit through the Earth's crust below a volcano, through which magmatic materials have passed. Commonly filled with volcanic breccia and fragments of older rock

http://www.geology.sdsu.edu/how_volcanoes_work/Volcano_types.html

For those who want it, this is an excellent site:
http://www.geology.sdsu.edu/how_volcanoes_work/volcano_links.html





Now back to my maths lessons!
K :)