* Pure Substance: A pure substance is made up of only one type of molecule. Examples include water (H₂O) or table salt (NaCl).

* Solution: A solution is a mixture of two or more substances where one substance (the solute) is dissolved evenly throughout another substance (the solvent). Salt water is a mixture of water (the solvent) and dissolved salt (the solute).

Since salt water contains two distinct substances, it's a solution, not a pure substance.