For those of you unsure of what this is, a sample CD is a collection of sound files that load into a sampler like Logicʻs EXS sampler, or Garageband Instruments, or NI Kontact. Samples are recordings of each individual note that an instrument plays. When they are loaded into a sampler, they can be played like a piano, but the sound will be that of the instrument that was recorded.

Loops are short 1, 2, 4,... bar performances of an instrument that when played will keep repeating. Drum and percussion loops are an easy way to build a rhythm track for your song.

Wikipedia explains it here.