Something is HEKDESH when you promise to give it to the Beit HaMikdash. If you decide not to give it, you must buy it back and then the money goes to the Beit HaMikdash!
So, if you make some bread HEKDESH you must give it, or its value, to the Bet HaMikdash. If you give its value, the bread- which is again yours- is called "redeemed (bought back) hekdesh."