Music sampling - Part 1: Definition

The Wiktionary definition of music sampling is:

a technique for electronically splicing pieces of previously recorded sound as part of a composition

The important thing to note about sampling is that it is different than copying (in the non-physical sense) a riff or tune from another work. If one can recreate the musical work of another without using the physical work, it is not considered sampling. Sampling, by definition, is not accidental.

Sampling is usually carried out through the use of a sampler, which can be a hardware device or software program.

Here's an example of a Yamaha sampler: http://www.savedbytechnology.com/main/yamahaA4000.htm