EFD and BFE are supplementary.
supplementary; either of two angles whose sum is 180°
The tiny square in the middle tells us that DB and AC are perpendicular.
Also, a straight line has the degree of 180°.
So, EFD plus BFE equals 180°.
Therefore EFD and BFE are supplementary.
Hope this helps!
If you need me to explain it a bit more, please let me know. :)