When you are being attacked one of the first things you will do to protect yourself is "irimi" (entering) or "tenkan" (turning).

"Irimi" - Enter. It can either be a slide or a step. Sensei will say or demonstrate the correct one for the technique.

"Tenkan" - Turn. The front foot remains in place, and you turn your body in the direction lead by your back foot's heal. It is a 180 degree turn (so you are now facing the opposite direction).

"Irimi Tenkan" - Step and then turn in one fluid movement.