What is osmolality?

In basic terms, it is the concentration of particles of a solution. For example, the osmolality of blood can be determined by its concentration of dissolved minerals like sodium, potassium, and calcium. When two solutions of varying concentrations are separated by a porous membrane, the higher concentration will flow towards the lower concentration until there is balance between the two. In the body, this process happens across a cell membrane, like from the small intestine into the blood.