Two polygons are said to be similar to each other, if:
(i) theircorresponding angles are equal, and
(ii) thelengths of their corresponding sides are proportional.
From the above, you can easily say that quadrilaterals ABCD and PQRS(shown below) are similar.
Here, we clearly see that each angle of polygon ABCDis equal to corresponding angle of polygon PQRS.