A rooftop is the flat or sloped top surface of a building where the roof meets the open air. While most people never go up there, rooftops serve important purposes: they protect everything below from rain and snow, they often hold equipment like air conditioners and water tanks, and in cities, they sometimes become gardens, playgrounds, or places to relax.

In crowded cities like New York, people sometimes transform rooftops into rooftop gardens where vegetables and flowers grow in containers, or rooftop parks where neighbors can gather. Some apartment buildings have rooftop decks with chairs and grills for summer cookouts. You might hear about a rooftop concert or see a rooftop solar panel installation that generates electricity from sunlight.

When someone says they're going up to the rooftop, they're heading to that flat or gently sloped area where you can stand and look out over the surrounding neighborhood or city skyline.