1. Lithops: This is the most common meaning. Lithops are a genus of succulent plants native to southern Africa. They are also known as "living stones" because they resemble small, smooth stones, blending seamlessly with their surroundings. They have two fleshy leaves that grow together, forming a split that reveals a flower during blooming season.

2. Living rock formations: This refers to rock formations that are covered in biological organisms like lichens, mosses, or even small plants. This can give the rock a green or textured appearance, making it appear "living".

So, when someone says "living rock", it's important to consider the context. Are they talking about a specific type of plant, or are they referring to a naturally occurring rock formation covered in life?