Tether is stable coin. Number of coins is valuation. Each coin is always 1USD (unless they loose the peg). So if 84 billion coins are there in circulation . 84

Tether is stable coin. Number of coins is valuation. Each coin is always 1USD (unless they loose the peg). So if 84 billion coins are there in circulation . 84 billion of dollars had been exchanged for coins . If the coins reduces to 73 billion then 11 billion coins have been redeemed back to dollars