In chemistry, precipitation means something different from when the weather forecaster on the news predicts rain. A precipitate is a solid substance that does not dissolve in a solution, and precipitation describes the process of the precipitate forming. This generally takes place when one or more soluble reactants in a solution undergo a reaction to form one or more insoluble products. The result is that a solid substance will form in a solution, either depositing on the bottom of the container or sometimes floating around in the solution. Depending on the circumstances, precipitation can be a desirable or undesirable result.