A portfolio investment entity (PIE) is an entity which invests the contributions from its investors in different types of passive investment.

The most common type of PIE is known as a multi-rate PIE (MRP). Investors in these PIEs will notify the MRP (via Snowball) of the prescribed investor rate (PIR) that relates to their situation. The MRP attributes income to the investor and calculates its PIE tax using the investor’s PIR. The MRP adjusts the investor's account by that amount of tax.

An open ended multi rate PIE means that the PIE is open to accept investments at any time, rather than having a finite window of time where it accepts investments.