Mixtures and solutions
A mixture is classified by whether its parts can still be seen: a mechanical mixture shows them, a solution does not.
A worked example
Salt stirred into water disappears from view and cannot be filtered out, so it is a solution, with water as the solvent and salt as the solute. Sand stirred into water still shows visible grains, so it is a mechanical mixture.
The mistake people actually make
A solution is always a mixture, never a pure substance, even though no parts are visible. Whether a solution is saturated depends on both temperature and how much solute has already dissolved, not on how it looks.