What does the rate of solution measure
how fast a substance recipitates
how fast a substance dissolves
how much of a substance dissolves
how much of a substance precipitates

I believe that the rate of solution is a measure of how fast a substance dissolves. The rate of solution depends on several factors which include; size of the particles, stirring, the amount of solute already dissolved, and temperature.
Considering the size particles, breaking a solute into smaller pieces increases its surface area and also increases its rate of solution, stirring allows the solute to dissolve faster and also increasing temperature increases the rate of at which the solute will dissolve and also the amount of solute that will dissolve.