There isn't really another name for the Law of Conservation of Momentum. It's a fundamental law of physics with a very specific meaning, so it doesn't have alternate common names.

However, you might encounter phrases like:

* The principle of conservation of momentum

* Newton's second law of motion in its most general form (since the law of conservation of momentum is derived from Newton's laws of motion)

These phrases are just ways of referring to the same concept: that the total momentum of a closed system remains constant over time.