Latin phrases pervade legal writing to the point where we use them so commonly they seem like part of the English language. A good example of this is the phrase ab initio, which means “from the beginning” or “from the inception.” For example: “Because it was unlawful, the marriage between cousins was deemed void ab initio.” In other words, a court’s declaration that a marriage was void would relate back to the moment it purportedly began.
— BBC&B