The term mmole is an abbreviation for millimole, a figure that is a part of the International System of Units and equal to 1/1,000 of a mole (SI). A mole is a unit of measurement commonly used in chemistry to denote amounts of atoms and molecules. One mole is equivalent to the number of atoms in .012 kilogram of carbon-12, making a millimole an extremely small amount.
A millimole of a substance is equal to the substance's formula mass (denoted in milligrams). Millimoles and moles are favored by chemists to show how much reactant and product are left after a chemical reaction. Molarity, a measure that denotes the number of moles that are dissolved in a liter of solution, describes how concentrated a substance is.