Definition - What does Solubility mean?
Solubility describes the degree to which a solute (any solid, liquid or gaseous substance) can dissolve into a solvent (any solid, liquid or gaseous substance) to form a solution (a combination of both solute and solvent created by dissolving the solute into the solvent) without leaving behind any undissolved molecules. Only ionic or charged compounds are soluble, and only a certain amount of dissolving can take place in one solution.
Safeopedia explains Solubility
Each atom has a certain number of electrons. Sometimes an atom gains or loses an electron and becomes an ion, which has an electrical charge. When an ion with a negative charge meets an ion with a positive charge, they join together like the positive and negative ends of a magnet. This is an ionic compound. Due to the unusual molecular structure of water, having both positively and negatively charged ends, ionic compounds which are bound together weakly are pulled apart when put into water and, therefore, dissolve.