Final answer:
The abbreviation NPO stands for 'nil per os' or 'nothing by mouth,' a directive used for patients who can't have food or drink before surgery or due to medical conditions.
Step-by-step explanation:
Residents with the abbreviation NPO on their diet cards cannot have anything to eat or drink by mouth. NPO stands for nil per os, which is Latin for "nothing by mouth." This medical directive is commonly used when a patient is preparing for a surgery or when their medical condition does not allow for oral intake to ensure patient safety and prevent complications such as aspiration. It's important for healthcare providers and caretakers to adhere to this instruction strictly.