It seems like you might be referring to a "rain head" or "rainwater head" in the context of gutter systems. A rain head is a type of fitting or accessory used in guttering systems to improve the flow and manage rainwater efficiently. Also known as a gutter collector box or rainwater collector, it is typically installed at the top end of a downpipe or downspout, where the water from the gutters is directed.
The main purpose of a rain head in a gutter system is to prevent debris, leaves, and other materials from entering the downpipe, ensuring that only water flows through and reducing the risk of blockages. It can also help to regulate the flow of water during heavy rainfall and provide an additional point of access for maintenance and cleaning of the gutter system.