A Liter corresponds to the amount of liquid that fits exactly inside a cube with 1 dm of edge. Since the density of water is approximately 1 kilogram per liter, this almost equivalence makes it easy to move from one measurement system to another (in the case of water). In other substances, whether liquid or not, the passage from one unit of measurement to another, is possible only if we know its density. As a matter of curiosity, know that filling a tub to take bath causes that approximately 265 liters of water are consumed, and that a liter of gasoline is enough to contaminate 700 thousand liters of water!
A Cubic Decimeter corresponds to the volume of a cube with 1 decimeter of edge. By volume, we mean the space occupied by a body or the capacity it has to store a certain substance, such as liquids. The cubic decimeter is widely used because of the ease with which this measure is converted to liters. This is because 1 cubic decimeter equals 1 liter, this makes the conversion instantaneous. Due to this equivalence between cubic decimeter and liter, this is the unit that should be used whenever conversions between these two volume measurement systems are desired.