A damaru is a small two-headed drum, used in Hinduism and Tibetan Buddhism.
The damaru is known as a power drum, and when played, it is believed to generate spiritual energy. In Hinduism, the damaru is known as the instrument of the deity Shiva, associated with Tantric traditions. It is said to be created by Shiva to produce spiritual sounds by which the whole universe has been created and regulated. It is believed that Sanskrit language was recognized by the drumbeats of the damaru, and his performance of the cosmic dance of tandava.
In the Tibetan Buddhist tradition, the damaru is part of a collection of sacred implements and musical instrument was adopted from the tantric practices of ancient India.
Reference - https://en.wikipedia.org/wiki/Damaru#:~:text=The%20damaru%20is%20known%20as%20a%20power%20drum%2C%20and%20when,the%20cosmic%20dance%20of%20tandava.
The damaru symbolizes the Universe which is always expanding and collapsing. From an expansion it collapses and then it re-expands, this is the process of creation.
If you see your heartbeat, it is not just one straight line but it is a rhythm that goes up and down. The whole world is nothing but rhythms; energy rising and collapsing to rise again. So the damaru signifies that. Look at the shape of the damaru, from expansion it collapses and again expands.
The damaru is also a symbol of sound. Sound is rhythm and sound is energy. The whole universe is nothing but a wave function, it is nothing but rhythms. What does quantum physics say? It says the same thing – the whole universe is nothing but rhythms. It is just one wave (Adviata). So the damaru signifies the non-dual nature of the universe.