Can someone explain retrogression?

I'm from India and my 140 got approved (EB1A). But I can't do 485 because of retrogression. I know that it means that I need to wait, but what exactly is retrogression? How long do I need to wait?

to wilma.andrews832:

I have an Indian friend who's also applying for a green card. This is what she told me.

When your 140 gets approved, the date you filed your 140 becomes your "priority date". You can only file 485 when your priority date is "current". I'm not exactly sure how long you need to wait, but you can probably check USCIS website to see which dates are "current" right now and get an estimate of how long you need to wait