XLR: A lockable connector, available with various numbers of pins (the most common being the 3-pin XLR). Often referred to as a "Cannon" after the original manufacturer of XLR connectors. More info: XLR connectors, Audio connectors
XML: Extensible Markup Language, a versatile markup language used in computer programming and web development. More info: XML
X-Y micing (X-Y pickup): A technique that uses two directional microphones aimed in an X or Y pattern to capture stereo sound.