A halved shape in the frame is when there is an object in the frame that has been cut out halfway by the edge of the photo. In this photo the tree is the object out of frame.

A skimmed edge or a hidden edge is when the edge of an object either fully or partially shares the edge of another object. In this photo the boy on the far left shares several edges with other objects in the photo.

A split apex is when vertical objects line up almost perfectly, creating an unseen line in the photo. In this photo there is a line of rocks directly in the center of the photo, as well as that they line up with a more defined part of the water in the waterfall.