A tongue of land projecting from high ground into lower ground is called a spur.

Here's why:

* Spur: This term specifically refers to a ridge or projection of land that extends outward from a higher elevation.

* Other possibilities: While other terms might be used in some contexts, they don't precisely fit the description:

* Promontory: A high point of land extending into the sea or a lake, often with cliffs.

* Headland: A point of high land jutting out into the sea, usually rocky and with cliffs.

* Cape: Similar to a headland, but can be more gradual and may not have cliffs.

Let me know if you have any other geographical terms you'd like to explore!