A few witnesses have mentioned that they have replayed after upgrading, while the documentation states that reindexing will be required.
Replaying and reindexing are the same thing.
I'm used to thinking of it as "reindexing" because that's what Bitcoin and BTS 0.x called it, so I'll often say "reindexing" when I'm talking / typing on autopilot. But "replaying" is the more "official" term used by Graphene and probably better describes what's actually happening (especially because Graphene has a ton more state than Bitcoin to support the markets, etc.)