There's a much bigger range of LED and specialty bulbs available in the ES27 (Edison Screw) base than the Australian BC22 (bayonet) base, but most light fittings in Australia use the BC22 base.
This adaptor solves this problem, allowing you to use an ES27 based bulb in standard Australian BC22 sockets. Just screw the bulb into the adaptor and you now have a BC22 based bulb!
Note: maximum current for this adaptor is 3 amps, but incandescent bulbs should be kept below 60 watts due to the heat they produce. It is aimed at use with CFL and LED lamps, rather than for use with incandescents. Design may vary slightly.