Certificates of deposit, or CDs, are fixed income investments that generally pay a set rate of interest over a fixed time period.
When referenced to the local common or ground, a common-mode signal appears on both lines of a two-wire cable, in-phase and with equal amplitudes. Technically, a common-mode voltage is one-half the vector sum of the voltages from each conductor of a balanced circuit to local ground or common.
In this situation the term common refers to the hot wire that is used any time the fixtures are lit as opposed to the travelers of the 3 way switches where only one or the other is powered at any one time. Any time a single hot wire powers a multi-position switch it can be referred to as the common conductor.