Input (grade 13): A bridge is a device for supporting the strings on a stringed instrument and transmitting the vibration of those strings to some other structural component of the instrument in order to transfer the sound to the surrounding air.
Output (grade 7): A bridge on a string instrument is something that stands on the body of the instrument and supports the strings. It sends the vibrations of the strings to the main part of the instrument so that the sound can be heard.