Probably the correct name ,
It would have two 90° angles ( the shape of the 🍞) and two others that add up to 180° , Then the top slice slides over the bottom piece dropping into and filling the slot, done properly the lower slice can still be lifted out by it's corner thus alleviating the need...
Cut the slice almost diagonally , the two 'triangles' load slightly apart and fit in ...
Note - they are not true triangles but I can't think of the correct word 😔