Here's a breakdown:

* Insoluble: The substance doesn't dissolve well in the solvent (usually water).

* Crystallizes out of solution: The substance forms a solid with a defined, repeating structure (a crystal) as it separates from the solution.

Example: When you mix a solution of silver nitrate (AgNO₃) with a solution of sodium chloride (NaCl), a white precipitate of silver chloride (AgCl) forms. The AgCl is insoluble in water and crystallizes out of the solution.