The time required for a signal from an input pin to propagate through combinatorial logic and appear at an external output pin.

In the Quartus^® II software, you can specify the required t_PD for the entire project and/or for any input pin, output pin, or bidirectional pin. You can also assign a point-to-point t_PD assignment to specify the required delay between an input pin and a register, a register and a register, and a register and an output pin.