![1girl breasts closed_mouth collared_shirt crossed_legs dated dutch_angle greyscale hair_between_eyes head_wings highres juliet_sleeves koakuma large_breasts long_hair long_sleeves looking_at_viewer monochrome necktie pantyhose pencil_skirt pointy_ears puffy_sleeves ruukii_drift shirt shoe_dangle shoes simple_background sitting skirt smile solo touhou very_long_hair vest white_background wing_collar wings rating:s score:12 post #3868107](/cdn_image/preview/3c/41/3c418e62e9eb8ca5aafed15aa9339436.jpg)
The picture is framed at an odd angle. Common to game CG where artists try to fit tall people and situations onto wide images, but don't want to put the images sideways. Term originates in filmmaking, also known as German angle or Batman angle.
Basically if you find yourself turning your head to one side in order to see the picture in proper perspective, this tag is appropriate.