The Scoville scale measures how hot a pepper or anything derived from peppers is to the human palette. The hotter the pepper, the more units it receives on the Scoville scale. The scale was invented by Wilbur Scoville in 1912.
As of 2015, the hottest thing on the Scoville heat units (SHU) scale are pure capsaicin and dihydrocapsaicin, which both come in at 16 million Scoville heat units. The hottest actual pepper on the Scoville scale is the Carolina Reaper, which comes in at 2.2 million SHU. The Bhut Jolokia comes in at just over 1 million SHU, while the Raja Mirch comes in at just under 1 million SHU. In contrast, a tangerine has no SHUs.