This button is used to send a request for quote to the exchange.
Some contracts are either not actively quoted or rarely actively quoted. In those cases, traders can request a quote from the exchange. The exchange passes the request to market makers, who in turn can put their orders on the contract, thus providing a quote. That quote is treated like a standard quote and is visible to all.
The system confirms the request before sending it.
You cannot request a quote for synthetic spreads or aggregation instruments.
To add this button, go to Trading Preferences > Trading Display > Enable RFQ.