Is there a word in English for a food eaten only partially out of hunger and largely for taste? Or perhaps for the act of eating for flavor rather than to satisfy hunger?
The first word that comes to mind is treat. From M-W dictionary (fairly far down on the page if you follow the link):
treat (noun): something that tastes good and that is not eaten often
As an example:
Your fresh chocolate chip cookies are a wonderful treat.
Such a food item is called a delicacy:
OED II.12.b.: Something that gratifies the palate, a choice or dainty item of food; a dainty.
Collins 3. (Cookery) something that is considered choice to eat, such as caviar.
Cate is a synonym, not actually marked as obsolete in OED but not really attested there since the 1870s.
goody (go͝od′ē) Informal
n. also goodie pl. goodies
Something attractive or delectable, especially something sweet to eat. FOD
Word associations show that many people react to the word "brown" with the instant response of "chocolate." It's a given that decadent goodies are usually a delicious chocolate brown (emphasis is mine.) Colors for Your Every Mood
decadent: characterized by or appealing to self-indulgence M-W
She slowly scooped a trail of chocolate from the plate with her finger, easing the decadent treat past her lips.
Eating for flavor, and more generally doing anything just for pleasure, is sometimes called indulgence, and this word has slightly negative connotations. (For instance, note self-indulgence). One sense of to indulge is essentially to do whatever you please, beyond some proper restraint.
But the question isn't about the action, but about a word for food.
However, indulgence can refer not only in the act, but also to the object of the act. That is to say, a morsel of something tasty is an indulgence.
This sense is corroborated by Merriam-Webster, which gives one of the meanings as "something that is done or enjoyed as a special pleasure".
All foods that have no dietary purpose are junk foods.
junk food, noun –Google
food that has low nutritional value, typically produced in the form of packaged snacks needing little or no preparation.
It's not a single word but it is 'a' noun and IMO, colloquially as close as you're going to get.
Look at all the junk food! What, not hungry? There's always room for Jello.
Snack (n.) a small amount of food eaten between meals
He had a snack of chips and dip. between-meal snacks I didn't have time for lunch so I just grabbed a quick/light snack. peanuts, potato chips, and other snack foods
A treat is usually something eaten only occasionally and could be eaten out of hunger. My three year-old son only eats when hungry, as far as I can tell, but when he is hungry he prefers what we call 'treats' over, say, a tomato.
An indulgence could also be eaten out of hunger, and Junk food often is. Although junk food has no nutritional value it is very effective at making you feel full, if only very temporarily. People often buy a burger or pizza precisely because they are hungry so I do not think junk food is the word you are looking for. The problem is that although the burger will fill your stomach it won't satisfy the body's needs, so you feel hungry again very quickly. So when you see people eating loads of burgers, that's not (necessarily) because they're being ridiculously indulgent, it may be because they are genuinely hungry.
There is no word that means exactly what you want, but an indulgence is as close as I can think of. I would recommend likening the food in question to some sort of food that is only eaten for taste, as a simile, although I can't think of a quintessential example. A related thing would be coffee, since nobody would drink coffee because they were thirsty, only for the taste.