What can i do to build definition on my biceps?

Work them: Do different types of curls and extensions. Eat right. And keep changing up your workout routine. Your muscles get 'used to' the same work out, so it is best to keep changing the exercises that you do. Use heavier weights with less reps. From personal experience, triceps are very tough muscles to bulk up. And they are even tougher to maintain. So keep at it. Good luck.