ID is a field that is filled automatically with a unique number when the record is created. The field value cannot be changed.

It is useful for updating participants using a unique identifier which does not change, for example if you want to manually re-assign bib numbers. 

When copying an event, ID numbering depends on the copy mode: with Next Edition, participants are not copied and ID numbers start again at 1 in the new event; with Full Copy, participants are copied and ID numbering continues from the original event.