The reference angle for an angle whose measure is -440 degrees is

Check the picture below.

if we go around the circle "clockwise", namely in the same direction as in a clock's hands, say -360°, that's going around the whole circle once, namely one revolution.  Now if we go further -80°, that'd be -360° - 80°, or -440°.

the reference angle is the angle made by that terminal point, with the x-axis, like in the picture.