A berry is a fruit that usually encloses many seeds of the plant. When berries are ripe, they fall off the plant. They are then still closed and juicy and are therefore also referred to by biologists as incipient fruits. If the fruit falls on good soil and stays there, the seeds will sprout. The new plant can start to grow.
But berries also have another task in reproduction: animals or humans eat the fruit. They usually cannot digest the seeds. So they are excreted with the feces and then grow in a far away place, the feces are there as fertilizer. This allows the plant to spread much better.
When we say berries, we usually only mean small, soft, sweet fruits, i.e. types of fruit such as raspberries, blackberries, strawberries, or currants. Soft fruit is also often strongly colored. Herbalists are stricter with the expression: For them, raspberries, blackberries, and strawberries are not berries. Botanists also count bananas, oranges, kiwis, or even melons among the berries. Even vegetables such as tomatoes, peppers, pumpkins, or cucumbers are berries.