What Exactly Counts as Tier 5 Equipment?

Q u o t e:
I know the sets purchased from the Scryers/Aldor, but what about other level 70 epic equipment? Just curious because I have heard that T5 gear is getting a buff.

Tier sets are specific sets of armor, some which include multiple variations. What a set is basically broken down to is the item's interaction with each other in the form of "set bonuses". The set bonuses only become available, or "turn on", when you have a certain number of that set. While other items may carry the same look as a set, and are sort of intended to fit into it to some degree to create a cohesive look, they aren't considered "tier items".

You can see the sets and the specific items in them here: http://www.worldofwarcraft.com/info/items/armorsets/

I'm not exactly sure what buff you're referring to, there are a couple changes that have been discussed somewhat recently that would affect Tier 5 stats.

Q u o t e:
I think he's referring to non-tier set loot that's on par with current Tier 5, i.e. stuff that drops in Serpentshrine that isn't a Tier set.

I would assume that too, but you never know. Also "the buff" is pretty vague, I'm not sure if it's affecting items other than tier 5 as I don't know what it is.