I would define a corner as any place where two walls (barriers?) meet at more or less a 90 degree angle. I’d also say those can be inner or outer corners, and both offer challenges. It’s easy for the dog to cut around those inner corners — e.g., to fail to push back into the corner of a room, and miss a hide back there. For the outer corners, the odor could channel along either side of the corner, making it more difficult to know exactly where source is.
Edges can be a lot of different things: the border between two different types of surface, the edge of a counter or wall, the edge of an object in the search area, the edge of a door or drawer. Odor may channel along an edge, or may fall to only one side of that edge, resulting in a confusing picture for the dog.