When chip manufacturers like Intel, TSMC, UMC, GF, etc. make wafers, there are slight variations in material quality across the wafer surface, there are local variations in how the lithography, metal vapor deposition, photoresist chemical deposition, etc. are done and this can yield a significant contrast between how good the best chip of a given batch will perform vs how bad the worst chip of the same batch will perform.
To maximize profit, chip manufacturers test and sort chips based on various criteria such as leakage current, power draw at key frequencies, salvageable defects, etc. to decide which product range the chips fit best in. That's binning.
When you buy "K-chips", you are playing the lottery: you are guaranteed a chip...