Depends on what you are referring to. Are you talking about the dead cap hit from prorated bonuses spread into void years? If so here is a quick overview;
Void years allow for teams to spread money (on the books) over future years, even the the player gets his money immediately. If a team allows a contract to void, all remained money left to pay that player in future years immediately becomes due. If they are extended or re-sign before the contract voids, then the dead money that was prorated can be remain in place until the contract eventually voids. Here is an example with Joey Bosa:
Bosa’s 9 million dollar signing bonus was spread out over 5 years, the maximum allowed by the NFL. So that 9 mill is split up at 1.8 a year from 2025-2030. Bosas cap his this year is actually smaller this year than next, despite not actually being under contract, because the void money of 1.8x4 years becomes due (7.2 million).
If they were to reach an extension or re-sign him, the void year’s signing bonus can remain at the 1.8 a year for the life of the contract. So if they give a one year extension, we in theory could save 5.4 money off of the dead cap next season.
Connor McGovern is another good example here, with 5 million in dead money next year because of void year signing bonuses for the next 3 seasons. they could save 2ish mill in dead money by extending him to allow void years to remain.