A sample is a digital representation of an analog signal. Both digital video and digital audio files are created using samples. The quality of the sample is determined by the sampling rate, or the bit rate the signal is sampled at.
What we see and hear in the real world is in analog format (our bodies process analog information). Computers, on the other hand, can only understand digital information. Therefore, audio and video signals must be converted to a digital format in order to be stored on a computer or saved to a CD or DVD. The converted data is called a sample.
The term "sample" is often used to refer to short audio clips used for playing back sounds. For example, a violin sound or a bird chirp may be sampled and then played back from a digital keyboard (or synthesizer). However, samples can refer to entire songs or movies, since the information is technically one long sample. To learn more about how samples are created, view the definition of sampling, which is the process of recording and creating digital samples.