Insoluble substance is a substance that does not dissolve in a solvent to give a reasonable concentration (e.g. chalk is insoluble in water).
Generalic, Eni. "Insoluble substance." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
Glossary
Periodic Table