* πέτρα (petra): This is the most common and general word for "rock," referring to a stone or piece of rock.
* βράχος (vrachos): This refers to a large rock, a crag, or a cliff. It implies something more substantial than a simple *petra*.
* λίθος (lithos): This word means "stone," and while it can be used for a rock, it's a more general term encompassing various types of stones, not just rocks.
Therefore, the best translation depends on the specific type of rock you're referring to. For most situations, πέτρα (petra) is a safe and accurate choice.