Is a strawberry actually a berry?

No.

A berry is defined as “a fleshy fruit containing several seeds.”

Strictly speaking, strawberries, raspberries, and blackberries are not berries, but aggregated drupes—a drupe being a fleshy fruit containing a single stone or pit.

Peaches, plums, nectarines, and olives are drupes. The world’s largest drupe is the coconut, which, because of its hard flesh, is called a dry drupe.

Strawberries, raspberries, and blackberries are called aggregated drupes because each individual fruit is actually a cluster or miniature drupes—the characteristic bumpy bits which make up blackberries and raspberries.

Each one of these drupelets contains a single tiny seed—these are the bits that get stuck in your teeth when you eat a blackberry.

Tomatoes, oranges, lemons, grapefruit, watermelons, kiwi, cucumbers, grapes, passion fruit, papaya, peppers, and bananas are all berries.