Katra stones were a type of stone found on Vulcan capable of blocking telepathic links.
Because of this characteristic, when Amanda Grayson sought to hide her son Spock, who was wanted on murder charges, she hid him in a sacred crypt containing katra stones, so any outside telepathic link would be prevented. (DIS: "Light and Shadows")
Katra stones presumably had some relation to katras and/or katric arks, as these all had some relation to telepathy.