While the common definition of a berry refers to small, seeded, edible fruit, the botanical definition of a berry is any fleshy fruit that is derived from a plant with one ovary and multiple seeds. Therefore, bananas are technically berries -- and so are tomatoes, kiwis, watermelons, and avocados.
Conversely, strawberries are characterized in botanical terminology as "accessory fruits," rather than berries, because they grow from tissue outside of the ovary. Raspberries and blackberries also aren't true berries, botanically speaking - they are classified as "aggregate fruits" because they grow close together from multiple ovaries and form a larger fruit.
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