Melee weapon attack with an unarmed strike

.@JeremyECrawford in most recent SA, you say that unarmed strike both is and isn't a weapon in consecutive answers. Which is it?

— Chris Cunningham (@devnuhl) November 28, 2015

In the PH errata, you can make a melee weapon attack with an unarmed strike (not a weapon): https://t.co/Uq1bZxECJw https://t.co/kTxUX4ThKa

— Jeremy Crawford (@JeremyECrawford) November 28, 2015