Solutions
In biology, a solution can be described according to its relationship with its external medium and the concentrations of solutes between the both of them:
-An hypertonic solution is one that has a higher concentration of the solute than its external medium.
-An hypotonic solution has a lower concentration of the solute than its external medium.
-A solution that is in equilibrium with its external medium is the one that has the same concentration of the solute as it.