The triceps is specifically at the back of your upper arm, opposite the biceps. She flexed her triceps to show how much she had toned her arms.
Pro Tip 2/3
Strength Training
Triceps are commonly targeted in workouts focusing on upper arm strength and toning. My gym instructor included a lot of triceps exercises in my new workout routine.
Pro Tip 3/3
Push Movements
Triceps are engaged in pushing actions, not just during specific exercises. You use your triceps when you push open a heavy door.