A gutter is a pipe or trough along the edge of a roof that carries rainwater away from a building. Another kind of gutter is the indentation beside a street curb. Water flows through these gutters too, usually into a storm drain.
The purpose of the gutters on a roof is to prevent water damage to a structure or flooding around its foundation. If your house has no gutters, water will run down the roof and drip from its edges. Over time, water can harm your house by rotting wood siding or trim, pooling beside its foundation, and seeping into your basement. A gutter directs the flow of rainwater away from the house, often into a drain or rain barrel.