Deletion is the death of a digimon. Their data in the digital world is "deleted." As to which the will dissapere pixel by pixel.

Deletion is always painful, the result of a fight gone too far. Most digimon will stop after the digimon has retreated, given up, or fallen uncontious or into a different stage. However there are fatal blows when the fight rages on too long and the digimon can not recover.

Once they have dissapered, they will "reboot" somewhere else in the digiworld and start life over. And will not remember much anything from their old life as the information was deleted in this process.

Sometimes that information can be restored, but in general is unlikely.