Bank Discount Basis

What Does Bank Discount Basis Mean?
A quoting convention used by financial institutions when quoting prices for fixed-income securities sold at a discount, particularly U.S. Government issues. The quote is presented as a percentage of face value, and is determined by discounting the bond by using a 360-day-count convention, which assumes there are twelve 30-day months in a year.

Also referred to as "discount yield".

Investopedia explains Bank Discount Basis
Differences in the day count convention used by the firm quoting a fixed-income security is subtle, but important. Over longer maturities, the day count convention will have a greater impact on the current 'price' of a bond than if the time to maturity is much shorter.

The 30/360 day-count convention is the standard when quoting government treasury bonds for banks.