nHz is Nanohertz 1/1,000,000,000 Hz (Billionth)

µHz is Microhertz 1/1,000,000 Hz (Millionth)

mHZ is Millihertz 1/1,000 Hz (Thousandth)

Hz is Hertz 1 Hz (Base Unit, one per second)

kHz is Kilohertz 1,000 Hz (Thousand)

MHz is Megahertz 1,000,000 Hz (Million)

GHz is Gigahertz 1,000,000,000 Hz (Billion)

THz is Terahertz 1,000,000,000,000 Hz (Trillion)

I suppose there are probably more that I’m not aware of, but I hope this clears it up.