Communications engineering. The pulse-amplitude modulation uses a pulsed carrier signal and an analogue (sinusoidal) modulation signal, which contains the information to be transmitted. The sampling of the analogue signal by the carrier signal produces pulses with different amplitudes. In terms like PAM5, PAM8 etc. the number means the number of amplitude levels used for the transmission. According to the sampling theorem the frequency of the carrier wave has to be at least twice the frequency of the analogue signal to ensure a safe demodulation by the receiver.
Pulse-amplitude modulation is used for baseband transmission, for example Ethernet.