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.
Staff were not washing their hands when required, or a handwashing sink was blocked, missing soap or paper towels, or used for something else. Hands are one of the most common ways germs reach food.
The business had issues with hot or cold running water, plumbing, drains, backflow prevention, or sewage disposal. Some of these, like no hot water, can force a temporary closure until fixed.