What is "unflag"

Usage examples of "unflag".

And he directed his comrade's attention to an unflagged area, just behind the bench on which they sat, that showed dark sandy loam and was large enough to have taken the passage of a broad-shouldered man.

Did Randolph think he could take passage on an unflagged merchantman to Tunis, and then march up to the gates of al-Idrisi's palace and throw down a glove?