A solvent is the substance into which another substance dissolves to form a solution. It is the largest part of the solution. Its counterpart, the solute, is the part that dissolves within the solvent.
Liquids or gases are potential solvents. Several rules apply to help determine which is the solvent and which is the solute in a given solution. First, the solvent is there in greater quantity than the solute. Secondly, the solute has a change of state when it dissolves. Water is often called a "universal solvent" because it dissolves so many different substances. This fact is especially important within the human body.