The key here is about food storage (more than food reheating)
Food needs to be stored properly BOTH before and after it is cooked.
The rule of thumb is referred to as the 4-2 Rule… the amount of time that food can safely exist in the temp range between 5 C (40 F) and 60 C (140 F)
Food out for 2 Hours OR Under, and one needs to either use it immediately… or store it below 40 F or cook it thru above 140 F
Food out for more than 2 Hours at either above 40 F or below 140 F is in the zone for not being the best to eat
And Food out for 4 Hours or longer in that zone… should be thrown out
So, for example, you bring straight home meat from the grocery store… your options are refrigerate it, freeze it, or cook it.
You make a pot of chili, and eaten some for Dinner… all the while letting the pot cool on the stove afterwards. If you cleaned up after Dinner and stored it at BELOW 40 F within 2 Hours and then reheat it to 140 F minimum the next day, then you are good to go.
IF you left the Chili out more than 2 Hours, you are taking a chance… more than 4 and you need to THROW IT OUT
OR if the next day you don’t reheat it to the required 140 F, you are taking a risk as well.
Also of Note, Leftovers (particularly those with meat in them) should not be eaten after 3 days of storage in the fridge.
So, if you are making a BIG Batch of Chili and may not eat it all within 3 Days, then break it down into smaller meal size containers for the Freezer.
And Items that were previously frozen, then cooked, should not be refrozen again… they then come under the leftover category… store them properly in the fridge for up to 3 days… or THROW THEM OUT
You can find more info on this stuff on-line by using GOOGLE… Government Food Agencies (like the FDA in the USA, or Health Canada) have websites that go into more detail
As well, you might consider purchasing a great Cookbook that has extensive info for NEW Cooks like the *Joy of Cooking*… it covers everything from setting up a Kitchen, Pantry Info, Cuts of Meat, Fruits & Veggies, Food Storage, Food Prep, Equivalencies, Entertaining, and YES even Recipes. Everyone who cooks IMO should have a copy… probably one of the best Kitchen Resources ever in print !!
Hope this helps,