Fab/fæb/ Definition 1 of 2Pro Tip 1/3Colloquial Usage Used informally among friends or in casual conversation, not in formal situations. Your new haircut is absolutely fab! Pro Tip 2/3Positive Intensity 'Fab' expresses a high degree of approval or enthusiasm about something. The party was fab, I had the best time! Pro Tip 3/3Emotional Expression 'Fab' often reflects genuine happiness or excitement about a situation or object. You passed your exam? That's fab!