convertible
A car with a roof that can fold down or be removed.
A convertible is a car with a roof that can fold down or be removed, letting you drive with the sky completely open above you. When the weather is beautiful, you can convert the car from enclosed to open-air in just a few minutes, usually by pressing a button or unlatching the roof. On a sunny afternoon, driving in a convertible with the wind rushing through your hair feels like flying close to the ground.
The roof might be made of fabric that folds neatly behind the back seats, or it might be a hard metal roof that slides away into the trunk. Either way, when you want protection from rain or cold, you can put the roof back up and drive normally.
You might also hear people describe other things as convertible when they can transform, like a convertible sofa that turns into a bed, or convertible pants that zip off to become shorts. Anything that can change its form or function to serve different purposes can be called convertible.