Mace is the sister spice to nutmeg. It's the dried webbing (aril) that surrounds a nutmeg seed, which means their flavors are very similar, though mace is subtler and less potent. Mace can be used like bay leaves and added stews and braises where the flavor can be extracted over a long cooking period. It can also flavor beverages and desserts, lending a softer flavor than nutmeg.
Note about refill bags: 1x refill bag size is the same volume as a large jar. 2x refill bag size is double the volume of a large jar. 3x refill bag size is triple the volume of a large jar.