I need resources that give the legal definition of leftovers.

According to Iowa Code 481-31.12 (137F), which is the code guiding
temporary food establishments and farmers market licensees, Part 2,
letter J, it says that leftovers may not be used, sold, or given away,
and hot-held foods that are not used by the end of the day must be
discarded.

What is the definition of leftovers? Is it possible to pre-cook food,
keep it cold, warm it up on-site and serve? Or is that technically a
leftover?

Thank you in advance for your help.

Here's some info from a U.S. Navy document:

"Leftovers
a. Leftovers are any unserved food remaining at the end of the meal
period for which it is prepared. Served food, or food that has been
placed on a serving line does not qualify and must be discarded.
Leftovers are categorized as potentially hazardous food and
non-potentially hazardous food.
b. Nonpotentially hazardous leftovers are such items as individual
commercially packaged crackers, condiments, etc., which may be
recovered from the serving line, but not dining tables or trays, and
be retained for reuse. Bottled condiments that do not require
refrigeration (e.g. mustard, catsup, steak sauce, etc.) may be
retained for reuse. Unsliced, hard skinned fruits may be retained from
serving lines for reuse provided they are washed.
c. Potentially Hazardous Leftovers. Potentially hazardous leftovers
include any potentially hazardous food prepared for a specific meal
period and then retained for a later meal period."

http://nepmu6.med.navy.mil/EH/P-5010-1(2).pdf