A quarter-inch jack, also known as a 1/4 inch jack or 6.35 mm jack, is a type of audio connector commonly used in various audio equipment. It features a cylindrical shape and is typically used for connecting instruments like electric guitars and amplifiers, as well as for headphones and speakers. The quarter-inch jack can come in two main types: mono and stereo, with the stereo version having an additional contact for a second audio channel. These jacks are popular due to their durability and ability to provide a secure connection. They are often found in professional audio settings, such as recording studios and live sound systems, as well as in consumer electronics. The quarter-inch jack is a standard in the music industry, making it an essential component for musicians and audio engineers alike.