When measuring anything, one needs to know the starting point and stopping point, and the measurement is the delta, or difference, between the two. When measuring electrical voltage, or potential, the starting point is usually, 0V, as referenced to ground (or neutral, which is likely the same thing).
In North America, the potential difference, in a single-phase system, between hot and neutral is 120V. The potential difference, in a split-phase system, between one hot leg and the other is 240V. The potential difference, in a three-phase, four-wire plus ground system, Wye connection, between any two of the three hot legs is 208V.
See also http://www.physicsclassroom.com/class/circuits/u9l1c.cfm .
In North America, the potential difference, in a single-phase system, between hot and neutral is 120V. The potential difference, in a split-phase system, between one hot leg and the other is 240V. The potential difference, in a three-phase, four-wire plus ground system, Wye connection, between any two of the three hot legs is 208V.
See also http://www.physicsclassroom.com/class/circuits/u9l1c.cfm .