# What is the amount of matter (g) within a specific volume (mL) called?

Do you refer to $\text{density?}$
$\text{Density}$ is $\text{mass per unit volume}$. It commonly has the symbol $\rho$, and typically has the units (for chemists) or $g \cdot c {m}^{-} 3$ or $g \cdot m {L}^{-} 1$.
And thus $\rho = \text{Mass"/"Volume}$.