pretty close. They're talking about designated "market makers" (of which specialists are a subset) who get into a contractual obligation with an exchange to be

pretty close. They're talking about designated "market makers" (of which specialists are a subset) who get into a contractual obligation with an exchange to be in certain markets for specified percentages of the trading day. They've been part of the exchange landscape for a long time, and they've been largely displaced by HFT firms. To say that this changing landscape is somehow to blame for the flash crash is dubious, at best, however.