Seraf references both the Realized IRR and Unrealized IRR of the investments in your portfolio to show the individual returns of each of your holdings. Realized IRR is the actual cash return on investments, computed for any investments that a) have some cash return and b) have either exited or have a net positive cash flow. Essentially it's the return on all cash in and all cash out over a period of time. The Realized IRR can be positive or negative but, like the XIRR formula in Excel, does not display when there is a complete loss.
Unrealized IRR is the same as Realized IRR, but assumes that you receive, on the date of calculation, cash equal to the current value of your remaining investment. It is the theoretical return that you would earn if you liquidated your holdings on the date of calculation. This may include the current value of companies (their associated rounds) and fund investments for which you’ve already realized some sort of return, as well as companies and fund investments that have yet to realize a return. Essentially it's the return on all cash in and all cash out including the current value of your holdings as though they were exited. Note that the system does not automatically assign a value to options and warrants, which are generally ignored for valuation purposes. For escrow and contingency assignments, the system uses the value assigned to them (i.e. the amount recorded or the number of shares times the share price recorded).
For more on IRR, check out:
Demystifying the Internal Rate of Return Measurement.