it is Diastasis Recti, and as previously mentioned a weakening of the fascia. May be cause by a large baby, or weak fascia to begin with.
There are many ways to get your abs back in shape and from my experience the fascia will not change much after being stretched.
Giving you exercises without seeing you will not have the same benefit. With that said: Find a pre/post natal or Pilates teacher that can help you getting your abs back in shape.