What is the name for the abdominal hernia received during pregnancy? where the two muscles come together and then seperate causing the hernia?

Rectus diastasis: This is when then rectus muscles separate or stretch apart during pregnancy. They almost always come back together by 6 weeks after delivery.

Diastasis : The two vertical bands of muscle (rectus muscles, aka 6 pack) that run form the breast to the pubic bone are joined by a thick narrow band of connective tissue. When this band flattens & thins, the band will bulge out when doing a sit up. This is called diastasis recti, or rectus diastasis. It is not a true hernia, as there is no hole through which abdominal contents can pass.

Ventral hernia: Muscles usually come together again after pregnancy. Occasionally do not in which case it's a ventral abdominal hernia. It is an umbilical hernia if confined to the belly button. These also usually resolve after pregnancy.