Food which is not chosen for its nutritious value, but rather for its taste, sugar, fat or caffeine content.
Although the term 'Junkfood' might refer to 'the food of junks', it is commonly eaten by people who have the financial means to purchase junkfood in large quantities, ranging from toddlers to senior citizens.
Junkfood is often eaten by people who are in a hurry, or by people who have 'the munchies'.
Also see junk food for some more information.
In general, its a good idea not to eat too much of these things mentioned in the above list. Its even healthier just to avoid junk food at all, and eat decent nutricious food such as carbohydrates-rich stuff like bread, potatoes and lots of vegetables.
Some example phrases:
"My son only eats junkfood!!"
"Junkfood is bad for you!"