Lump charcoal is whole pieces of wood that have been exposed to high temperatures, which drives out chemicals and leaves only carbon.  The charcoal itself is not pre-formed and as a result is in different shapes and sizes.  Briquettes are carbon that is ground up annd mixed with fillers before getting pressed into standard shapes.

Since lump charcoal is free of fillers, it is cleaner burning and leaves less ash than briquettes. Lump charcoal also burns hotter than briquettes and using vents on grills, it's easier to control the temperature using lump charcoal.   

My one friend is a frequent griller and smoker.  He prefers lump charcoal since it is cleaner and he can control the temperature.  He's had to buy other brands of lump charcoal since he didn't see any offered by Kingsford.  We are both loyal Kingsford fans and would purchase Kingsford lump charcoal if it was available.