XTAL:  Quartz Crystal / Crystal resonator
XO:  Fixed-frequency uncompensated Crystal (Clock) Oscillator
VCXO:  Voltage Controlled Crystal Oscillator
TCXO:  Temperature Compensated Crystal Oscillator
TCVCXO:  Temperature Compensated VCXO
VCTCXO:  Voltage Controlled TCXO (same as TCVCXO which is the better term)
OCXO:  Oven Controlled Crystal Oscillator
VC-OCXO:  Voltage Controlled OCXO
TC-OCXO:  Temperature Compensated OCXO
RbXO:  Rubidium Crystal Oscillator
EMXO:  Evacuated Miniature Crystal Oscillators