Your normal term deposit, the bank is issuing the payment of interest on the deposit (you're dealing with the bank). In a PIE investment, you're lending to a 3rd party (not the bank directly but a managed 'Fund') that will invest for you. The distinction and marketing ploy on PIE is the overall tax with a PIE investment is lower tax of 0.25% or less depending on your marginal income bracket vs if you invested in a term deposit, the tax with-holding % would be in the tax bracket you're in.
For fixed income investments, there's not a lot to worry about the difference. The real problem with PIE is when invested in equities (shareholdings of companies) as under PIE, these managed fund re required to pay the FDR 5% tax EVEN ON YEARS THAT ARE NEGATIVE RETURN.