Someone who knows a little more will come along but the big difference is that lump charcoal is just burned wood (charcoal). Briquettes are charcoal dust held together with a binder (starch) and usually have borax (in minute quantities) or something else in them to help them release from the briquette mold.
Briquettes are usually very even burning and all the briquettes burn at basically the same rate because they’re the same size and density.
Lump charcoal is made of different size pieces that can cause its burn characteristics to be vastly different from one piece to another. Lump also tends to provide a little better flavor. Lump tends to burn hotter and faster.
Thanks.
I guess the best way to find out is to try some lump charcoal to compare to the briquettes. I'll just pick up a bag at Home Depot and give it a go.