teag1rl - This bigger bit is fat (Assuming this is not scar tissue from c-section? in which case we dealing with something completely different)
However if it is fat then people underestimate how low a persons body fat % needs to be in order to achieve a flat tummy and waist area. This bit is often the last part to go as many have more fat storage cells in this area.
Measuring and monitoring is key to see continued progress in the battle to lose fat and keep muscle. Without it you simply guess if your doing the right thing and often people go months and months getting no closer to their goals, eventually giving up with the idea that they have the wrong genes that makes them fat.