The mace is a heavy medieval war club with a spiked or flanged metal head, used to crush armour. Note that real maces are prohibited in NSW. The point of it was to emulate a club, but with more weight and, optionally, the sharp edges of the spikes or flanges for concentrating force. Both infantry and cavalry used them -- the horseman's mace tended to be shorter in the shaft, for easier wielding; the footman's longer for added power (albeit at the expense of speed).
Maces are believed by some to be primarily for incapacitating opponents. This was particularly useful in an age where ransoms could greatly enrich a person.
The mace is considered a mass weapon, and therefore must conform to the rules that govern all mass weapons. The head must have at least half an inch of progressive give between the striking surface and the haft. The striking surface must also have rounded edges. Any striking thrusting tip must be at least two inches wide.
Mace is an aromatic spice that originally came from East Indonesia. Dried and leathery, mace has a very similar flavour to nutmeg, which isn't surprising. They're both sourced from from the same plant - nutmeg is the kernel of the fruit, mace is the lining that separates the kernel from the pulp.