The reactions in which a more reactive element displaces another element from its compounds are called displacement reactions.
2Al(s)+2NaOH(l)+6H2O(l)⟶2Na[Al(OH)4](s)+3H2(g)
The reaction of aluminium with sodium hydroxide gives a salt and hydrogen gas. In this reaction, aluminium displaces sodium from its compound, therefore, it is a displacement reaction.