Endothermic reaction: In endothermic reaction, heat is either absorbed from the surroundings or heat has to supplied from outside. It means an endothermic reaction needs or takes in heat to continue.
For example: When a solid ammonium chloride (NH4Cl) is dissolved into water, you will observe that the tube becomes colder.
NH4Cl (s) + H2O → NH4Cl (aq) – Heat
In the above reaction, heat is absorbed from surroundings.