In heraldry, a compartment is a design placed under the shield, usually a landscape or wreath of some sort upon which the supporters are depicted as standing. It is a comparatively late feature of heraldry.
Usually when arms are augmented by supporters, a compartment will be added too.
... 1 - Glenn Miller, bandleader (+ 1944)
March 2 - Dr. Seuss, author (+ 1991)
March 8 - Victor de Kowa[?], actor (+ 1973)
March 6 - Joseph Schmidt[?], tenor (+ 1942)
...