Which term describes the size of the signal?

The correct term that describes the size of the signal is amplitude. In the context of electronic signals, amplitude refers to the maximum extent of a vibration or oscillation, measured from the position of equilibrium. It indicates the strength or power of the signal; higher amplitude implies a stronger signal while lower amplitude indicates a weaker one. This is a crucial aspect in telecommunications and audio electronics, where signal strength can drastically affect the quality of transmission and reception.

The other terms listed relate to different characteristics of signals: frequency refers to how often the signal oscillates in a given time, phase describes the position of the wave in its cycle at a specific time, and waveform refers to the shape or form of the signal over a period. While these are all important properties of electronic signals, they do not pertain directly to the measurement of the signal's size.