The 'Breast' of a Mantel refers to the horizontal portion over the firebox opening which is typically supported by the Mantel 'Legs' or by Corbels. In some instance the Breast may simply be mounted to the wall on a hidden cleat (see our 'Mantel Shelves' category for examples of this).
The top of the Mantel Breast is typically the widest point of a Mantel and is referred to as the Mantel 'shelf'. This is where most people like to place decorative items or seasonal and/or Holiday ornaments.