the parent poster means simply betting against their customers. Not explicitly shorting a security without a locate. Just a lingo thing. In any case, this so

the parent poster means simply betting against their customers. Not explicitly shorting a security without a locate. Just a lingo thing. In any case, this sounds a lotvlike a Contract-for-Difference type of arrangement. The broker functions as the liquidity provider, taking the contra side to all customer bets. Broker collects the bid-ask spread and hopes that it overcomes losses. One big downside is counterparty risk: if the broker goes bankrupt, the winning customers may not get paid!