Answer in Details
One of the well-known references is the Eleven Rudras (Ekadasha Rudra). These are eleven different manifestations of Rudra, each with distinct attributes and energies. The names and roles of the Eleven Rudras may vary across texts, but they are generally considered as multiple forms rather than a single avatar.
So, the Rudra avatar is not a single form—it represents many forms of Lord Shiva, embodying his fierce and transformative aspects.