[tcoppi]

There doesn't need to be an official BTC-USD tether, BTCUSD on bitfinex is exactly that in practice and in fact.

[alexpetralia]

That's not a tether though, that's an exchange rate.

A tether is like a fixed (pegged) exchange rate[1], where there is an arbitrage opportunity. But that's not BTC-USD.

[1] https://en.wikipedia.org/wiki/Fixed_exchange-rate_system

[dwaltrip]

BTCUSD floats freely, based off the latest trade. It's not pegged.