The torr is a non-SI unit of pressure, named in honor of the Italian physicist Evangelista Torricelli, who invented the mercury barometer. One torr is defined as 1/760 of an atmosphere, which is approximately equal to 133.32 Pascals. A smaller unit derived from the torr is the millitorr (mTorr), with one torr being equivalent to 1,000 millitorr. Torr and millitorr units are primarily used for measuring low-pressure environments, such as those found in vacuum systems.