The key difference between eutectic and eutectoid reaction is that in eutectic reactions, a liquid transforms into two solid phases at the same time whereas in a eutectoid reaction, a solid transform into two other solid phases at the same time.

What is eutectoid and eutectic point?

Eutectoid is used to signify that the liquid phase in a eutectic phase diagram has been replaced by a solid phase. Otherwise the eutectoid and eutectic definitions are identical. For example, in steels the solid gamma phase undergoes a eutectoid reaction to become a lamellar mixture of alpha and cementite.

What is the difference between eutectic and peritectic?

The difference between eutectic and peritectic is that eutectic is describing the thermodynamic equilibrium conditions where a liquid coexists with two solid phases while peritectic is describes the isothermal reversible reaction of a liquid phase and a solid phase to form a second solid phase during cooling.