The solid is more tightly packed, more dense than the liquid. But, because the crystal form of water contains lots more empty space, it is less dense than the liquid form. There is less mass per volume. The liquid water is more dense than the solid water - which is why ice cubes float on water. Units of density are, for example, grams per milliliter, pounds per cubic foot, kilograms per liter.
Water is a great solvent.
You can dissolve things into it. Water is the solvent and sugar and flavoring are the solutes . If you add too much solute, more than the solvent can dissolve, the solute will begin to fall out - the solution is saturated . The amount of solute in the solution is a measure of the concentration . A unit of concentration is, for example, grams of solute per liter of solvent.