Hatch

Official wording

Properly scaled and calibrated thermometer or thermocouple not provided or not readily accessible in food preparation and hot/cold holding areas to measure temperatures of TCS foods during cooking, cooling, reheating, and holding.

In plain English

Food was not kept cold enough, hot enough, cooled fast enough, or cooked or reheated to the right temperature. Bacteria grow quickly in the "danger zone" between 41°F and 135°F, which makes this one of the most important food-safety checks.