Item ID allows a custom ID to be auto generated upon the created of each new list record. Using dynamic patterns, you can create more meaningful IDs than the standard SharePoint ID field which is always a simple integer.

It is recommended that when you setup your Item ID that you use a prefix that holds the something like a Year or month value. The actual numerator function for the Item ID can accept up to 2 parameters, such as [#|n|m], where n is the seed value and m - number of digits.

Note: When running the Item ID process on a column that has no previous prefix values (the prefix if wht is before the [#|n|m] the Item ID will use the seed value to start the series and all subsequent Item ID (triggered on the edit or new) with genrerate the next value in the series. 

However, when running the Item ID process on on records where there is a previous prefix value and there are gaps in the number series (ie a record was deleted) then this will back fill any gaps in the series that it can use, until all gaps are filled. 

For example, if we have old record that is 2024-00001 and that record is delete that record, then later we edit a record that has no Item ID, that edited record will run the edit Item ID process and reuse 2024-00001 as the item id for this record.