The number of moles of solute present in $1\text{kg}$ of a solvent is called

Molality ($m$) is defined as the number of moles of solute dissolved per kilogram ($1\text{kg}$) of the solvent.
$$\text{Molality }(m)=\frac{\text{Moles of solute}}{\text{Mass of solvent in kg}}$$

Molarity ($M$), on the other hand, is the number of moles of solute per liter of solution.