A HIN is a unique number that is issued by the Australian Securities Exchange (ASX) when you become a client of a broker. All shares that you buy through that broker will be connected to your HIN.
You can find your HIN on a CHESS statement. A HIN starts with the letter X and is followed by ten numbers, e.g. X0001234567.
To offer lower brokerage rates, some entities may use an omnibus (rather than an individual) HIN to hold shares. This means investors are not the legal owner of their shares and they have fewer protections (including being able to claim against the National Guarantee Fund) if something goes wrong.
If you hold shares through an omnibus arrangement, be sure to look at the terms of the arrangement to understand how your shares are recorded and how corporate actions like voting rights are handled.