Yes, cucumbers are botanically a fruit. While they are probably one of the last plants that we would think of as a “berry,” that is what they are botanically. (Specifically, they fall under the botanical subclassification of fruits called a “pepo.”) This classification is because cucumbers have seeds inside them, are fleshy, were made from a single ovary, and don’t split open to spread their seeds everywhere. They are the “fruit” of the plant. However, this definition of fruits is just largely independent from our everyday culinary definition. Cucumbers can be a fruit botanically and a vegetable culinarily. Practically, cucumbers are not fruits.
In the culinary world, they are obviously considered to be vegetables.</span> They are mainly eaten in leafy vegetable salads, not fruit salads. They aren’t sweet; they are largely flavorless. These show that cucumbers are vegetables. If you put cucumbers in your berry pies, you should probably be committed. I have never heard of someone considering cucumbers to be fruits. They are vegetables.
How can something be both a fruit and a vegetable?