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.
XLS:
Script designation for extra long shot, AKA extreme long shot, extreme wide shot (EWS).
More info: EWS, Shot types