A strawberry is not an actual berry, but a banana is.
It’s probably rare that you hear a banana, avocado, or pumpkin referred to as a berry, but the fact is they are. It seems like people generally consider a berry to be a small fruit that comes in bunches, but in reality there are several definitions for what people call berries.
There are drupes, which are fleshy fruit produced from a single seeded ovary with a hard stony layer, like peaches, plums, and cherries. Olives also fall into this category. There are pomes, which are fruits that have a structure that separates the seeds from the ovary tissue, like apples and pears. Some of the smaller pomes are also called berries sometimes.
There are aggregate fruits like the blackberry and raspberry, which are fruits that contain seeds from different ovaries of a single flower. There are multiple fruits, which are fruits that are made from multiple flowers packed together, like the mulberry. Lastly, there are accessory fruits, where the edible part is not generated by the ovary, which includes the strawberry.
So by these definitions, a strawberry is not a berry. A berry is simply a fruit that has seeds and pulp produced from a single ovary. In addition to those already said, this includes the blueberry, coffee berry, cranberry, gooseberry, grape, persimmon, and tomato.
By technical definition, a berry is a fleshy fruit produced from a single seed. The strawberry, however has its dry, yellow “seeds” on the outside (each of which is actually considered a separate fruit). True berries, such as blueberries and cranberries have seeds inside. However, the banana fruit is a berry for the same reason strawberries are not.
There is a theory that strawberries were named by 19th century children who picked the fruit, strung them on grass straws, and sold them as “Straws of berries”.