"Vertical incision" refers to a cut or opening made from top to bottom, often used in medical procedures, usually along the length of the body. Full definition
Your previous cesarean incision was a low - transverse uterine incision (which is horizontal) rather than a vertical incision in your upper uterus (known as a «classical» incision) or T - shaped, which would put you at higher risk for uterine rupture. (babycenter.com)
A vertical incision is sometimes used during emergency c - sections. (bellefit.com)
(If you have a vertical incision, it's unlikely that you'll be able to attempt a vaginal delivery with your next pregnancy.) (babycenter.com)