NMOS with a resistor(load) at drain is also a inverter.
PMOS " " " " " " " " "
Driver- potencial control over state of circuit.
Load-imposes the possible control line to the driver.
By this nomenclature NMOS or PMOS can be Driver.
In CMOS, all people knows that PMOS drive well 1, NMOS drive well 0.
When MOS drive is like a switch, then offers small resistance.
When MOS load is like a current source, then offers high resistance
by tradition and usualy, load connected between output and VCC,
and transistor which drive output load locate between ground and output (LOAD).
therefore transistor at ground side named DRIVER and transistor at VCC side named LOAD.