The Unreserved Fixed Rate is a certain type of deal in programmatic advertising.
Transactions that fall into this category, exist in an exchange environment as well as Automated Guaranteed, Invitation-Only Auctions and Open Auctions. Unlike Invitation-Only and Open Auctions, Unreserved Fixed Rates have got a pre-negotiated, fixed pricing (CPM, CPC, etc.).
Typically, Unreserved Fixed Rate Deals, sit at a higher priority than Open Auctions and Invitation-Only-Auctions. This type of deal is typically used by advertisers with a demand for more predictable offerings within the exchange space.