is what is being dissolved in a solution, and a does the dissolving. A solution is composed of a solute being dissolved in a solvent.
If you have a glass of water with sugar in it the water is the solvent and the sugar is the solute. The solvent is always the larger quantity, as in this example you always have more water than you do sugar or else not all of the sugar would dissolve.
Also, it does not really matter if both are liquids ; the one in greater quantity is the solvent.
Meaning, you can have a complete gaseous solution (one gas as solvent and another as solute.) Or even a gas dissolved in a liquid solvent (example carbon dioxide in many beverages.)