What quadrilateral has 3 equal angles?

There is no specific name for one with 3 equal angles. All the interior angles in a quadrilateral add up to 360°. So you would have 3A + B = 360. Where angles A = C = D. Now a rectangle has 4 equal angles (90°), so it also has 3 equal angles. And just happens to have the 4th angle equal the other 3.

To visualize a quadrilateral with only 3 equal angles: take a square ABCD, and stretch angles A,C & D to 91°. Now angle B will equal 87°.