noun
BAD : The shop sells fruits and vegetables.
GOOD : The shop sells fruit and vegetables.
BAD : I never buy tinned fruits.
GOOD : I never buy tinned fruit.
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Fruit (= fruit in general) is an uncountable noun: 'We eat lots of fruit in our family.' 'Would anyone care for a piece of fruit?' (= an orange, apple, pear etc)
Fruits (= particular types of fruit) is rarely used in British English.