What is Bond Equivalent Yield?

Legal Definition
The bond equivalent yield or BEY for an investment is a calculated annual percentage yield for an investment, which may not pay out yearly. It is not to be confused with a bond's coupon rate. This allows investments which payout with different frequencies to be compared.
-- Wikipedia
Legal Definition
When income is sold from a bod at a discount. The difference between par values and purchase price for two bonds are made into a percentage. AKA coupon equivalent rate and equivalent bond yield.