(unit of pressure approximating a millimeter of mercury on Earth)
A torr is a unit of pressure defined as 1/760 of an atm.
It was originally defined as, and is meant to approximate the
pressure associated with 1 millimeter of the mercury column in a
mercury barometer. Torr is not an SI unit but is based on one.
Note: the word for the unit is torr (non-capitalized), but the symbol
is Torr (capitalized), so 1/1000 of it can be written as a
millitorr, with the associated symbol, mTorr.