A forms B which in turn is converted to C, then the reaction is called as 

Composite reactions may occur in different ways. Consecutive or sequential reactions are one type of composite (or) complex reactions.

Ex: $\text{A}\stackrel{{\text{K}}_{\text{1}}}{\to }\text{B}\stackrel{{\text{K}}_{\text{2}}}{\to }\text{C}$

Here A forms B (intermediate) which in turn is converted to C.