VCXO (Voltage Controlled Crystal Oscillator) is a crystal oscillator, whose frequency is determined by a crystal, but adjusted by an external control voltage applied to the input. This is commonly used in an IC Clock generator.
Below is a typical diagram of VCXO CLK generator.
TCXO (Temperature-Compensated Crystal Oscillator) is a crystal oscillator that has a high-precision, with a temperature-compensated network included to maintain a more constant frequency during the temperature variations.
Sometimes TCXO is used in case the frequency stability of the tradition XO falls beyond the needs over a standard or extended temperature windows. TCXO are widely used in cell phone or wireless application. High-end TCXOs are also important components in telecom and other industries.