That is the key date in terms of your citizenship application. Your citizenship application clock starts ticking from it.
This date is determined by USCIS and represents the day when USCIS entered your application into their system. It is not the mailing date, signature date or postal recival date, but simply the date when their employee had a time to enter your case in the system.
USCIS is using this date to measure the time passed since you've applied. Actually, this date puts you in a certain class....like a college graduation class.
You can use this date to compare how is your application being processed compared to other applicants on this forum.
