My ab definition is visible at arouund 15-16%. Clear at 12%. However it's not something I'm overly fussed by. About having perfectly cut and chiseled abs. I don't see the obsession with them. I'd much rather have a functionally strong core and not give a toss what mine look like. Yeah they're nice to look at and mine were developed enough, for me, last time I cut down to 12% body fat with minimal/almost no isolation work.
Just like I'd rather have boulder shoulders or quads of doom!
The obsession with abs is something I associate with teenagers.
Not Ab bashing anyone who has lots of goals one of which is to have visble abs, but anyone that has the sole goal of 'I want to loose my gut and have a six pack' who then spends 5 days a week on the ab craddle and then rolling around on the mats like a retard needs to sort it out imo.