Combination or synthesis.
A synthesis or combination reaction is a type of chemical reaction in which two or more simple substances combine to form a more complex product. The reactants may be elements or compounds. The product is always a compund.
A synthesis reaction can be represented by its general equation: A + B → AB
In this case:
4AI + 3O2>2AI2O3
We have a combination between Aluminum and Oxygen, where the new compound is 2AI2O3.
