A kitchen triangle is located in very standard kitchen. It is when the sink, stove top, and refrigerator are laid out in the shape of a triangle. Those three items are shaped as a triangle because it is said to be good for better efficiency.
A closet is pretty much an area in a room that has doors on the outside to close it off from the rest of the room. A closet acts as storage for anything you can possibly need. A closet can be located in any room but is mainly in bedrooms, bathrooms, and the pantry is a type of closet.