In production, a sample is a stored fragment of audio that a sampler, drum machine or DAW plays back on command, usually when a pad is struck or a MIDI note arrives. It can be tiny, like a single snare hit (often called a one-shot), or longer, like a four-bar phrase lifted from a vinyl record.
The word has a second, technical meaning in digital audio: one individual measurement of a signal’s level at a given instant. These measurements are taken tens of thousands of times per second, 44,100 times at CD quality. Jazz lo-fi tracks are often assembled from samples in the first sense: drum one-shots, chopped melodic phrases from old records and textures such as vinyl noise. When a sample comes from someone else’s recording, its use normally has to be cleared with the rights holders.