Molarity? Molality?

Units of chemistry are case-sensitive! A 6 M solution of a compound refers to a 6 Molar dilution, which has a concentration of 6 moles soluter per liter of solution. A 6 m solution refers to a 6 molal dilution, which has a concentration of 6 moles of solute per kilogram of solution. Molarity and molality may be equivalent in some situations, especially if the solvent used to make the solution is water (where a liter weighs about a kilogram). However, the terms and the solutions aren't usually interchangeable. Here's a handy reference defining the units of concentration and here's a set of worked example problems for molarity.