Amplitude vs. Instantaneous Amplitude

peak amplitude (often shortened to simply ``amplitude''): the nonnegative value of the waveform's peak.

instantaneous amplitude: the value of $x(t)$ (either positive or negative) at any time $t$.

A sinusoid with an amplitude of 2 is illustrated below.

Figure 5: Sinusoid where $A=2$, $\omega = 2\pi 5$, and $\phi = \pi /4$.