BBSY stands for "Bank Bill Swap Yield". It's a reference rate used to calculate the interest rates ona variety of financial products, including
securitisations. BBSY is calculated as the average of the yields on overnight indexed swaps (OIS) that are denominated in Australian dollars and have a tenor of 3 months.
BBSY is a more reliable reference rate than the previous Australian reference rate, BBSW, because it's not as susceptible to manipulation. OIS are collateralised transactions, which means that the cash flows between the two parties to the transaction are guaranteed. This makes OIS less susceptible to manipulation than other types of interest rate swaps, which are not collateralised.
The use of BBSY as a reference rate has made securitisations more attractive to investors. This is because BBSY is seen as a more reliable and transparent reference rate than BBSW. As a result, securitisations that use BBSY as a reference rate are typically able to attract lower interest rates and are more likely to be successful.