A single value in a digital signal, which represents an instantaneous voltage level in the corresponding analog signal. A digital signal consists of a stream of such words, which represent a succession of voltage levels which would make up an analog signal. The analog signal can actually be realized by processing the digital signal through a D/A converter.
The two basic characteristics of a digital signal are the word rate (the frequency at which words are to be converted to analog by a D/A converter, or were originally converted from analog by an A/D converter), and the word width. The frequency which is half of the word rate is the Nyquist frequency, which is the highest frequency that the digital signal can contain. The word width is measured in "bits"; the number of bits determines how precisely each word can represent the corresponding analog voltage. Common word widths in current sampler and digital synthesizer designs are 16 and 24 bits; older samplers used 12 or 8 bits. (The original Fairlight CMI was an 8-bit system.) Roughly, each additional bit of precision results in a 5 dB improvement in the signal-to-noise ratio.
Digital signal processing engineers commonly use the term sample to mean a digital word, a usage that stems from the use of a sample and hold circuit in most types of A/D converters. However, in music, there is a conflict with the use of "sample" to mean a sound recorded by and stored in a sampler. So musicians usually avoid using "sample" to mean a digital word.