Nut is a general term for the large, dry, oily seeds or fruit of some plants. While a wide variety of dried seeds and fruits are called nuts in English, only a certain number of them are considered by biologists to be true nuts. Nuts are an important source of nutrients for both humans and wildlife.
A nut is a type of seed. Nuts are both the seed and the fruit, and cannot be separated. Seeds come from fruit, and can be removed from the fruit, like almonds, cashews and walnuts which have to be extracted from the fruit. Some nuts as defined in culinary usage like pistachios, are not true nuts in a biological sense.
The grouping of many similar dry seeds and fruits under the single generic name "nut" is not followed in many other languages, which have only individual names for each type.