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Something like $\frac{a}{b}$, split by $-$, we call $a$ Molecular, $b$ Denominator.

$$\begin{align*} f(x) &= x^2 \\ \\ &\Downarrow \text{Take derivative of the previous formula} \\ \\ f^\prime(x) &= 2x &(x^2)^\prime &= 2x \\ \\ &\Downarrow \text{Take derivative of the previous formula} \\ \\ f^{\prime \prime}(x) &= 2 &(2x)^\prime &= 2 \end{align*}$$

We say $f^\prime(x)$ is the first derivative of $f(x)$, $f^{\prime \prime}(x)$ is the second derivative of $f(x)$. You can keep doing this by changing the number before derivative, for example, 3 derivative of ...