Diaphragm

n.
  1. A dividing membrane or thin partition, commonly with an opening through it.
  2. (Anat.) The muscular and tendinous partition separating the cavity of the chest from that of the abdomen; the midriff.
  3. (Zoöl.) A calcareous plate which divides the cavity of certain shells into two parts.
  4. (Opt.) A plate with an opening, which is generally circular, used in instruments to cut off marginal portions of a beam of light, as at the focus of a telescope.
  5. (Mach.) A partition in any compartment, for various purposes.
    6. Diaphragm pump ,
    one in which a flexible diaphragm takes the place of a piston.