Final answer:
The term 'Low sugar' is not a defined nutrient content claim, while 'low fat', 'low sodium', and 'low calorie' are officially regulated claims.
Step-by-step explanation:
The term "Low sugar" is NOT a defined nutrient content claim by regulatory agencies like the Food and Drug Administration (FDA). Claims like "low fat", "low sodium", and "low calorie" are officially defined and regulated. Foods can be labeled as "low" in a nutrient if the percent daily value of the nutrient is 5% or less. However, "low sugar" does not have an official definition or specific criteria established by these regulatory agencies, making it not a defined nutrient content claim.