What's a Sample?
A sample is a digital recording of a sound. In the context of this conversation, the PC3K (like the K2X00 series) can load and play back external wave data -- as opposed to the PC3X, which can only play patches created from its own internal wave ROM (onboard sample set).
However, neither the PC3K nor the PC3X are true samplers, in that neither can record samples from an external source (i.e. through a mic or line input).