X The electronic symbol for reactance - the imaginary part
(don't worry about it) of impedance.
XLR® Registered trademark of ITT-Cannon. The original model
number series for Cannon's 3-pin circular connectors - invented
by them - now an industry generic term.
XOR Acronym for exclusive OR, a type of logic gate
where a logic 1 output is based upon A or B inputs being present
- but not both.