There are regions where ships can travel at faster-than-warp speeds, such as Warp Region 6 and a transwarp conduit. There are regions like the Briar Patch where warp drive is not possible. Warp-normal describes regions where warp travel is neither unusually fast nor unusually slow—in other words, most of the known galaxy.
Root speculates that the USS Enterprise is especially suited to charting Warp Region 6 because it is fast enough to recover should a boundary fluctuation dump it in warp-normal space. (TOSS #18 "The Ends of the Earth")