I guess your question is more whether you can SEE a ‘six-pack’ rather than having one. As Joanne points out, it is the structure of the muscle itself that makes it look like this.
I believe, though, it may be wise to differentiate between men and women here. Not so much in terms of ‘six-pack’ but in terms of body composition required to make it visible. While guys can safely drop their percent body fat to the point where they can admire the famous silhouette, women may have to drop down to levels which are no longer healthy.