Suppose there are $N$ waves, say, $\psi_1\text{,}$ $\psi_2\text{,}$$\cdots\text{,}$ $\psi_N\text{,}$ in a region of space at some time $t$>. Then, according to the superposition principle, their sum will give us the net wave we will observe in that region.
$$\psi = \psi_1+\psi_2+\cdots+\psi_N.\tag{14.8.1}$$