A substance that cannot be dissolved in solution is called insoluble.

Here are some other terms you might come across:

* Immiscible: This term is usually used for liquids that don't mix, like oil and water.

* Nonpolar: This refers to the chemical structure of the substance. Nonpolar substances tend to be insoluble in polar solvents like water.

* Precipitate: This refers to a solid that forms when two solutions are mixed and a substance becomes insoluble.

Let me know if you'd like more detail on any of these!