What is the medical term for a sideways curvature of the spine?

Scoliosis is where the spine twists and curves to the side. It can affect people of any age, from babies to adults, but most often starts in children aged 10 to 15. Scoliosis can improve with treatment, but it is not usually a sign of anything serious and treatment is not always needed if it's mild. Many people will not need any treatment and only a small number will need to have surgery on their spine.

Source: NHS