The US FDA uses common words to mean something different. FDA evaluates certain terms with reference to a typical portion size known as an RACC (Reference Amounts Customarily Consumed). An RACC of eggnog, for example, is ½ cup. For croutons, it’s 7 grams, and for scrambled eggs, 100 grams. Many labels use artificially low or high portion size to reduce or increase the amount of calories, fat, etc. perceived by the consumer.
Imitation - A food only has to be labeled as “imitation” if
it has a lower amount of protein or some other essential nutrient
than the food it’s trying to look like.
Free - To be labeled “free” of calories, the food must have
less than 5 per RACC. For fat and sugar, less than .5 grams. For
sodium, less than 5 milligrams. Also, the food must somehow be
processed to be “free” of those things in order to get the simple
“free” label. You can not have “fat free lettuce,” only “lettuce, a
fat free food.”
Low - Low is also defined with respect to set portion sizes
and varies with whether it refers to calories, fat, or sodium. For
fat it’s less than 3 grams. For calories, it’s less than 40, unless
it is a prepared meal, in which case it’s 120 per 100 grams.
Reduced/less - Sometimes manufacturers want to make a
relational claim about a food—not just that it’s “low” in some
substance, but lower than it usually is (which may mean it doesn't
meet the standard for “low”). Relational claims are evaluated with
respect to a reference food. A reference food should be the same
type of food, as yogurt vs. yogurt. The “reduced” substance must be
less than 25 percent of what it is in the reference food.
Light/lite - This is also evaluated with respect to a
reference food, and a rather complicated set of conditions is taken
into account for different substances. For example, if a “light”
product has more than half of its calories from fat, the fat must be
reduced by half per reference serving amount. If less than half its
calories come from fat, it can be “light” if the calories per
serving are reduced by 1/3. Sometimes foods that meet “low”
requirements can also be labeled as “light.”
High - High means that the food has 20 percent or more of the
recommended daily value for that nutrient per reference serving.
Good Source - “Good source of” is a little lower than “high.”
A food with this label should have 10 to 19 percent of the
recommended daily value.
Lean - “Lean” applies to seafoods or meats that have less
than combined specified levels of fat, saturated fat, and
cholesterol (10g, 4.5g, and 95mg, respectively).
Natural - The FDA has not established an official definition,
but endorses the general understanding that it implies nothing
artificial or synthetic has been added that would not normally be
expected to be added.