First a die crack is a small break on the die.

Note the image on the lack left. See how small the die crack is? The crack allows to show a raised area on each coin struck by that die. Thus a small area is affected.
Well sometimes more of the die will break off of a crack and show what we call a die chip:

You can see near the 'M' where more of the die is chipping off and leaving a void. So a void on a die will leave a raised area on each coin struck by that die. Sometimes the die will chip without a crack and leave a void. These are also called die chips:




So the chip you are seeing is often the amount that broke off the die leaving a void. The ones that are flat on the tops is where the void when so deep into the die, that the planchet can out of material to fill that void. We often see this on
Cuds:

Note the first image the die on the right is what a
Cud looks like on a die. If would not have enough metal to fill that void, thus they are flat on the tops of these
Cuds.



This one is a double
Cud. But something interesting about
Cuds is that opposite the area where the
Cud is, there is a void not filled because of the missing resistance during the strike. Do you see these voids? These are where the opposite side has the voids/cuds on the coin. But most of the things mentioned, while interesting, are not real collecables as they are common. But the last one mentioned,
Cuds are collectable and very desirable as just a few are created as the die has reached the end of it life. So I hope I fill in a few space of information for you. If not, ask another question.