What's the difference?
fruit and fruits
Oh yes. A casual look at the many websites that cater for learners of English must count this example as one of those that get many hot under the collar (an idiom that means to become anxious and angry, but often unnecessarily).
But this is as I, and many of my colleagues here at TEE Towers, interpret the word, incredibly without having to pull each others' hair or resulting in serious injuries through canteen food fights.
First, the good news. In most cases, either form can be used to describe the plural of more than one fruit. Second, British English speakers tend to use fruit more than fruits to describe more than one kind of fruit. We often say 'a bowl of fruit' (a bowl that contains many different kinds such as apples, bananas, oranges, etc), and 'I enjoy fresh fruit for breakfast' (one or more different kinds that we eat for our first meal of the day). If someone asks you if you would like any fruit, they are giving you a choice of one or more different kinds to eat.
But if you want to say fruits to mean more than one, then this is perfectly okay.
Probably the reasons for the confusion lies with the fact that as we usually buy all our plant produce from the same shop, we all tend to say vegetables to mean more than one vegetable. When you get these vegetables from the ground, they are usually individual and not one of many vegetables growing from the same bush or tree, unlike fruit. And fruit contains seeds or stones from which you can grow more fruit bushes and trees. And when we put them all together, we (in the UK, anyway) think of the word as an uncountable noun, even if we can count them - just as it is still possible to count two buses, seventeen cars, five trucks and four vans and use the uncountable noun to describe the one group as traffic.
1. When we talk about a specific tree/bush, and we give a name to the fruit that is growing on them, e.g. apple, grape, etc., then we count them: There's a lot of apples on my tree. The grapes produced in Portugal this year are excellent.
2. In British English at least, when we talk about many different kinds of fruit presented as mixed ingredients in, for example, joghurts and fruit juices, we use fruits: there are several fruits in multi-vitamin drinks. But when we talk about fruit where it is presented as one of many pieces of different kinds of the same fruit, we say just that: this salad contains many pieces of fruit (but you can still say fruits if you want, rather than pieces of fruit).
3. When we talk about trees and bushes that bear fruit, we mean that the plant concerned has successfully produced many of the same kind of fruit. To say that they bear fruits may suggest that they are producing more than one kind of fruit - rather like a citrus plant especially cultivated (meaning specifically grown) to produce both lemons and limes.
4. To bear fruit is also an idiom, meaning that something is successful and is producing good results.
5. Then we have dried fruit (fruit that has been preserved by having the water removed), and forbidden fruit (a source of pleasure from doing something you should not be doing, like arguing about all this on a forum). Both can be countable or uncountable.
6. Fruit is also a verb to describe a plant that produces fruit: My trees are fruiting.
And while we are on the subject of fruit and vegetables, tomatoes, bean pods, pumpkins, peapods, aubergines (egg plants), olives, butternut squash, red, yellow and green peppers, courgettes (zucchini) and even cucumbers are definitely fruit, but are often used in vegetable cooking. Likewise, rhubarb is usually used for sweet cooking, but in fact are the long leaves and red stems of a vegetable. Avocados, carrots, and sweet potatoes, which are all vegetables, can be used to make cakes and desserts.
And finally, we will kill off one myth. Many people have heard that a banana is technically a herb, not a fruit! It's the 'technically' part that people do not pay attention to. The yellow thing you eat is definitely a fruit, but the tree (which is not really a tree) contains a stem that is not made up of tissue that we would expect to be wood. This type of plant is known as a herbaceous plant, or a herb.