MOSFET ON and OFF current
For PMOS and NMOS, the ON and OFF state is mostly used in digital VLSI while it acts as switch. If the MOSFET is in cutoff region is considered to be off. While MOSFET is in OFF condition there is no channel formed between drain and source terminal. When MOSFET is in other two regions it is ON condition and there is a channel formed between drain and source terminal. We deduce on and off condition by VGS, VDS and Vt inequalities(as shown in below figures). Once you know the region of operation you can apply the appropriate current formula to find out current.

Regions in which PMOS and NMOS can operate: