An "arco" is a term that can refer to a variety of concepts, but it is most commonly associated with a type of musical bow used in string instruments. In this context, it describes the technique of playing string instruments like the violin or cello using a bow, which consists of a stick with horsehair stretched between its ends. The bow is drawn across the strings to produce sound, allowing for a range of dynamics and expressions. In architecture, "arco" is the Italian word for "arch," which is a curved structure that spans an opening and supports weight above it. Arches are commonly found in buildings, bridges, and other structures, providing both aesthetic appeal and structural integrity. They have been used since ancient times, with notable examples found in Roman architecture.