Four corners of the earth
All parts of the Earth.
From the Miles Coverdale's Version of the Bible, Revelation 7-1:
And after that sawe I foure angels stode on ye foure corners of the earth, holdinge ye foure wyndes of ye earth, yt ye wyndes shulde not blowe on ye earth, nether on ye see, nether on eny tree.
A similar expression is found in Isaiah 11-12:
And he shal set vp a toke amonge the Gentiles, and gather together ye dispersed of Israel, yee and the outcastes of Iuda from the foure corners of ye worlde.
The reference to four corners does not imply that the writers of these texts believed that the Earth was flat (although they may well have done). the first citation above suggests more that the four corners were the four compass points.