The difference is the cooking process. Traditionally, Souvlaki is cooked using pork (but we have used lamb) and kebabs are cooked using lamb. Souvlaki is cooked horizontally on a spike, but a kebab is cooked vertically on a spike. Souvlaki also has a different marinating process than kebabs. If you go to Greece and order a kebab, you will get souvlaki.