TCXO, Temperature Compensated Crystal Oscillator
As the name indicated a temperature compensated crystal oscillator provides a means of counteracting the frequency change caused by temperature change in a crystal oscillator.

The letters TCXO stand for Temperature Compensated Xtal Oscillator - Xtal is short from crystal and implies a quartz crystal resonator. The TCXO module is able to provide considerably improved performance over that of a standard crystal oscillator, especially in terms of frequency stability over a temperature range.

By measuring the temperature and applying a correction voltage to a VCXO, the frequency stability over a temperature range is considerably improved whilst keeping costs low - using an oven controlled cryst