Exactly Sparky66!
With respect to the number of phases that a particular system has, for all practical purposes we are really refering to the number of sine waves present. With single phase, we have one sine wave. If we could slow time down and look at the current flow on a single phase circuit, at a point where current is flowing "IN" one of the conductors, you can bet the farm that it is flowing "OUT" the other.
Because we only have two conductors that we can measure a potential difference between, we can only have one single voltage. The amplitude of the voltage is the same throughout the circuit at any point in time.
Conversely, on a 3 phase system we have three seperate sine waves. If we superimpose these sine waves over each other, we would see that each phase is typically 120 degrees out from the next.
Matt
