A cucumber is a long, green vegetable that grows on a vine and tastes cool, crisp, and refreshing. Cucumbers are mostly water inside, which makes them perfect for hot summer days. You've probably eaten cucumber slices in salads, on sandwiches, or alongside other vegetables with dip.

Cucumbers belong to the same plant family as melons, pumpkins, and squash. Like their relatives, they start as flowers on climbing vines before growing into the familiar green cylinders we eat. Some cucumbers are smooth and dark green, while others have bumpy skin. The bumpy ones are often turned into pickles by soaking them in vinegar and spices.

People sometimes say someone is as cool as a cucumber when they stay calm under pressure. This phrase comes from the fact that the inside of a cucumber can stay cooler than the air around it, even on a hot day. So when your friend stays relaxed during a difficult math test while everyone else is nervous, they're being cool as a cucumber.