Clydesdale, AC voltage is normally specified as the "RMS" (root-mean-square) value. The explanation for this is a little complex, but it basically means that a 120 volt RMS AC source will provide the same power (wattage) as a 120 volt DC source to the same resistive load.
For sine-wave AC, the peak voltage is the RMS voltage times the square root of 2, or 1.414 times the RMS voltage. A 120 volt "hot" conductor alternates between +170 and -170 volts.
