This rate refers to the rate that Westpac Banking Corporation will sell foreign currency bank notes (cash) and Travellers Cheques to you, in exchange for Australian Dollars.
Example - You are about to depart on a holiday to England and would like to have some English Pounds in your possession when you arrive. Westpac Banking Corporation would use the Note sell rate to convert your Australian Dollars into English Pounds so you can carry either Notes or Travellers Cheques with you.