The molarity of a substance is a scientific way to talk about how concentrated it is. Molarity describes the number of moles of the substance per liter of liquid.
In chemistry, a mole is a unit of measurement for a chemical substance. The scientific noun molarity describes the concentration of a substance as measured by the number of moles divided by the volume of the solution it's in. So a chemist might talk about the molarity of Sodium Chloride in a liter of water. Molarity comes from mole, which was coined by a German chemist from Molekül, German for "molecule."