Shabd jab tak vakya me prayog na ho jaye tab tak shabd kehlata hai.Shabd jab vakya me prayukt hota hai toh veh vakya ke niyamo se bandh jata hai.Vakya me prayukt hone ke baad shabd koi na koi prakarya avashaya karta hai.Prakarya karne ke karan hi shabd "PUD" ban jaata hai.