CV/gate is made up of two components. The control voltage indicates which note to play, and the gate indicates when a note should start and stop. In the case of triggering a drum machine, a clock signal or LFO square wave could be employed to signal the next beat (or rest).
There were a number of variations on the basic CV/Gate interface. The most widely-used was that employed by Roland. Roland's implementation used a logarithmic voltage signal of 1 volt per octave. The Roland gate is a positive going signal, called a voltage trigger (or v-trigger) that is usually low-voltage and becomes high while the note is being played. Oberheim, Sequential Circuits and Arp Instruments also used the Roland standard.
The 1990s saw renewed interest in dated analog synthesizers and various other equipment, notably the Roland TB-303. In order to facilitate synchronization between these older instruments and newer MIDI-enabled equipment, the CV/Gate-MIDI interface was invented.