Li Shenron
Legend
But an unarmed strike is any melee weapon attack where you're not using a weapon?
I don't think so, there are many cases of melee weapon attacks:
- melee weapon
- unarmed strikes
- objects as improvised weapons
- specific spells
The "melee attacks" section of the PHB combat chapter doesn't call them "natural attacks" but mentions monsters using claws etc separately from weapons, so it could be read either way as an important or unimportant distinction. But certainly not everything which is not a weapon in chapter 5 is automatically an unarmed strike.
There is too little about "natural weapons" in the books to be sure they are their own thing to be added to the list above, but they are however mentioned explicitly so neither it's sure they aren't.