= Waveform
A <waveform> specifies how a wave-related quantity varies with time or position. For an electrical recording it may be $V(t)$, an <electric potential difference>; for <sound> it may be the <sound pressure> $p(t)$. Both the shape and its physical scale matter: a normalized trace alone omits amplitude and time units.
For example,
$$
s(t)=\sin(2\pi ft)+\tfrac13\sin(6\pi ft)
$$
contains a fundamental <frequency> $f$ and a third harmonic. It has the same period $1/f$ as the first sinusoid but a different shape. Varying the relative phase of the third harmonic changes that shape even when the two component amplitudes stay fixed. A <Fourier series> describes periodic waveforms through such harmonic amplitudes and phases.
A microphone and oscilloscope can record an acoustic waveform after calibration. The recording is also affected by the instrument's <frequency response> and <signal sampling>: a narrow-band microphone smooths sharp features, and inadequate sampling can misrepresent oscillations. The observed waveform therefore represents the signal together with the measurement chain.
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