Learning Experience, The

Official wording

Accurate thermometers not available or used to evaluate potentially hazardous food temperatures 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.