Concentrated and Dilute
Concentrated solutions have more solute per unit volume than do dilute solutions. A company may pour concentrated industrial waste into a river in order to "dispose" of it. The waste is still there in diluted form, of course. Very low concentrations may be called trace amounts.

Solubility, Saturated and Unsaturated
There is usually a limit to how much solute will dissolve in a solvent. When this limit is reached, the solution is said to be saturated. This limit may be expressed in grams/100 mL of a specified solvent such as water or ethyl alcohol. The value is only valid at the specified temperature given. We always have to hedge a bit when using the term insoluble, since most solids will dissolve at least a little bit in a solvent such as water. Example: Is sand (silicon dioxide) insoluble in water? Ask a geochemist and the answer may surprise you.

Supersaturated Solutions
If you evaporate a saturated solution to remove part of the solvent, or cool a saturated solution, you may produce a solution with more grams per mL than the given solubility. The solution is metastable, however, meaning that the extra solute will eventually drop out of solution given either time or an external disturbance.

Miscible and Immiscible
Some liquids such as water and ethyl alcohol can be mixed in any proportion to make a solution. These are miscible. "Oil and water" is the traditional example of two liquids that are immiscible. Small amounts of one liquid usually dissolve into the other, however.