This is a knotted Rudraksha Mala. Rudraksha is considered as incarnation of Bhagwan Shiva. The person who wears Rudraksha possess a good health, is respected by all and leads of prosperous life.
It is also a kind of shield against negative energies. Atharva Veda and Shiva Puraan mention how Rudraksha helps to get positive energies to your advantage to lead a happy and prosperous life.