Consider my pictures at various body fat percentages:
The body fat percentages where my abs are clearly visible is between 8-10%
However, if you are even more muscular or have worked very hard to makes your abs blocky, especially the lower abs, you can get better visibility even when you are between 11-12%
In the end, it really depends on what kind of look you prefer.
If you want slightly visibility of abs and a flat tummy, at the same time, you want a balanced lifestyle where you are not obsessed with working out and eating super clean, then maintaining a 12-15% body fat percentage is ideal.
But if you desire a clear, well defined six pack look and are willing to give up some of your favourite foods than you need to go below 10%
Hope this helps:)