what are multisampled CDs?

dudes.

i am about to ask a completely basic question. i would really appreciate it if someone could answer me it with the most easy to follow explanation:

i am looking into getting an MPC4K but would like to know what are multisamples & multisampled CDs

a multisample piano fi is a program with all the notes beeing mapped accross the keyboard. (CDEFGAB, CDEFGAB, etc)