Honestly, if you don't care about the depth of the separation, you just need to exercise and eat properly on a regular basis in order to achieve definition. But, if you seriously want those little buggers to shine, then we need to perform spinal flexion exercises to grow the rectus abdominis; make it thicker. I can't speak for women, but I know most men like that deep cut in their abs. Though it may look like separate muscles (4, 6, sometimes 8 depending on the individual), it's one muscle separated by bands of connective tissue.
So why am I giving this information away for free? Why don't I just bundle it up in a nice little package with some fancy graphics and a price tag to match? Two reasons: 1) This is stuff you already (or should already) know but have either forgotten or are avoiding because you know about reason number two. 2) Hard work and discipline don't sell. There is no magic pill or shortcut to the abs you want. I guarantee you everyone promoting otherwise is lying to your face. So, you can either spend time year after year going from one fad diet or program to another (continuing to be frustrated), or you can take that same amount of time to do it properly and in a way that should last you a lifetime.
I've said it before and I'll say it again: Strength is made in the gym, physique is made in the kitchen. Basically, grow your muscles in size and strength in the gym and let what you put in your face be the vehicle to trimming away the fat so you can see what you've accomplished. Yes, it's a pain in the butt, but so is going in circles and spending tons of money. The hard way is not always the right way except when it comes to health and fitness. I don't write these articles for my health; I write them for yours. :-) Now, go get it!