It's an outflow from Coinbase wallet by block. When this indicator goes over 10,000 bitcoin, it is usually likely to go to Coinbase Custody Wallet for OTC transactions since Coinbase Custody is directly integrated with Coinbase's OTC desks. And lots of U.S. institutional buying has been delivered by Coinbase Custody, including Grayscale.
Tokens Transferred refers to the total amount of Bitcoin that has moved on the network. Fund Flow Ratio is the amount of Bitcoin used for deposits/withdrawals on the exchange divided by tokens transferred.
If the Tokens Transferred is high, and the Fund Flow Ratio is low, it might indicate OTC transactions are active. For example, when the Bitcoin price was ranging $10k in 2020, 4 million Bitcoin ($40B) moved on the network, where only 3% of the transactions took place on the exchange, and 97% of the transactions took place outside the exchanges. After that, many institutions announced that they had purchased Bitcoin, including Microstrategy, Ruffer, One River, etc.