noun

• (mycology, chiefly US) Bioluminescence created by some types of fungus, particularly those growing on rotting wood.
  "The foxfire,—as the country people call it,—glowed hideously from the cold and matted bosom of the marsh; and, far from us, in the depths of darkness, the screech-owl sat upon his perch, brooding over the slimy pool, and whooping out a dismal curfew, that fell upon the ear like the cries of a tortured ghost."
• (by extension, loosely) Wood exhibiting fungal bioluminescence; torchwood.
  "On the inside is fixed a Barometer, by which he can tell the depth he is under water; a Compass, by which he knows the course he steers. In the barometer and on the needles of the compass is fixed fox-fire, i.e. wood that gives light in the dark."