The descriptions you provided relate to the concepts of saturated and unsaturated solutions, as well as supersaturated solutions in chemistry. Here are the corresponding definitions for each description:
a. Saturated Solution: A solution with as much dissolved solute as it can hold at a given temperature. No more solute can be dissolved.
b. Concentration: The amount of one substance in a certain volume of another substance.
c. Supersaturated Solution: A heated solution that holds more dissolved solute than is possible at a lower temperature.
d. Unsaturated Solution: A solution that holds less solute than is possible at a given temperature. More solute can dissolve.