What is the baptize of this hip bath piece? There is triangular shaped piece of plastic in the corner of hip...

There is triangular shaped piece of plastic in the corner of hip bath right where the tub meet the wall. It was installed within by the former owner of the home and its purpose as best I can tell is to save water from leak onto the floor. It is about 6 inches by 6 inches. Does anyone know what this is call and where I can draw from a new one?