A solution is defined as a homogeneous mixture, normally in the liquid phase, in which the components are uniformly intermingled. Any part, or any sample of a solution is identical to the others. A solution consist of a solvent and a solute . The solvent is the component present in the largest amount.
Water is always the solvent in aqueous solutions.
The solute is the part dissolved in the solvent. The solute can either be a solid, liquid or gas. In order to have a solution, the solute must be soluble in the solvent. Water is polar, so polar compounds are expected to be soluble in water. Small polar covalent compounds are expected to be water soluble.