depends on your definition
at it's simplest a sample is a recording of something that you use to make a composition with
there are two somewhat orthogonal usages though.
1st usage is that of musique concrete where you use recorded sounds to make new pieces of music; this includes sample libraries of orchestral and other acoustic instruments, as well as other sounds found in the environment: trains, planes, cars, trucks, boats, whistles, bells, sirens, explosions, guns, kissing, people speaking, laughing, crying, screaming, sexual acts, etc.....
usage two is to use a small section of an existing musical as the basis of a new musical such as poor boy, which samples Bohemian rhapsody by queen