What is molality?

In chemistry, the concentration of a solution refers to the amount of solute dissolved in a solution. There are various ways to report concentrations depending on the units used. Some of the most common ones are molarity, molality, and percentages. Percent of a solute can be weight by volume (w/v) or weight by weight (w/w), which is simply the ratio of the mass of the solute to the total volume or weight of the solution.
Molarity and molality makes use of the ratio of the moles of solute to either the volume (in liter) of solution or the mass (in kilogram) of solvent, respectively. Molality is most often used in experiments that involve a significant change in temperature as molarity is sensitive to temperature due to expansion/compression that may result to significant changes in volume - and hence, apparent concentration.
In brief, molality is one way to express the concentration of a solution. It is the ratio of the number of moles of solute to the mass in kilograms of solution:
m = (n_(solute))/(mass_(solvent)) .