Load Capacitance in CMOS Circuits
If you don't have a load on the circuit output then the circuit doesn't do anything useful. So, we don't care very much about that case.
The output of any CMOS logic circuit is normally connected to the input of some other logic circuit. The wiring between the two circuits is part of the load on the first circuit, as is the input capacitance of the second circuit. The &quot;load&quot; on a CMOS circuit can usually be modeled as just the capacitance of the wiring and the gate capacitance of the driven CMOS circuits. If the wire is relatively long then it may be necessary to treat the wire a a distributed RLC network instead of a lumped capacitance.