If it is the panel I think you are talking about, then it is definitely a PACK exhaust air exit vent. The A380 has it's PACK's in the leading edge of the wing at the root. You can see the cutouts in these photos.
Many A and B aircraft traditionally had the packs in the belly fairing, but this is by no means standard. I don't recall which aircraft it is exactly, but either the L-1011 or DC-10 had its PACK's under the flight deck floor.
JetMech split the back of his pants. He can feel the wind in his hair.