Thermite is a mixture of iron oxide and

Mixture of metal oxide and Al powder in 3:1 ratio is called Thermite mixture.

Mixture of BaO₂ and Mg or Al powder is called ignition mixture.

Example for thermite mixture is, Fe₂O₃ and Al  3:1 ratio.

→ On burning of Mg-ribbon, it carries the flame into ignition mixture.Ignition mixture on ignition provides huge amount of energy.By using this energy Al of thermite mixture reduces the metal oxide to metal. The metal obtained in this process will be in liquid state .This formed liquid metal (Fe) is used for welding of train rails and welding of other metals.