Apparently "defined abs" can be mimicked by using liposuction in a procedure called "abdominal etching."
Lots more information at Plastic and Reconstructive Surgery. Image cropped for size from the original.
The authors found an overall complication rate of 8.6 percent (206 patients). The most common complications were contour irregularities (71 patients), seroma formation (54 patients), hyperpigmentation (36 patients), asymmetry (18 patients), hypertrophic scar (15 patients), chronic induration (six patients), skin necrosis (four patients), and infection (two patients).Via Neatorama.