An LNG train is a liquefied natural gas plant's liquefaction and purification facility.
For practical and commercially viable transport of natural gas from one country to another, its volume has to be greatly reduced. To do this, the gas must be liquefied (condensed) by refrigeration to less than -161 °C (the boiling point of methane at atmospheric pressure). This process requires strict safety precautions during all liquefaction stages, due to the flammability of the gas.
There are numerous impurities that freeze at low temperatures that are found in raw gas. Since these would block the cryogenic section of the plant, the gas must be purified before it can be liquified.