A `supervisor` in Elixir is responsible for monitoring and managing child processes. It ensures that if a child process crashes, it can restart it according to specified strategies.

In Elixir, a supervisor plays a crucial role in maintaining the robustness and reliability of applications by monitoring and managing child processes. Supervisors are part of Elixir's supervision trees, which are designed to handle process failures gracefully. When a supervisor starts, it initializes its child processes according to defined strategies, such as one-for-one, one-for-all, or rest-for-one. The one-for-one strategy means that if one child process crashes, only that process will be restarted. The one-for-all strategy, on the other hand, will restart all child processes if one fails, while the rest-for-one strategy will only restart the crashed process and any processes that were started after it. This hierarchical structure allows for better fault tolerance and recovery mechanisms in your applications. When implementing a supervisor, you typically define a module that uses the Supervisor behavior and implement the required callback functions. This enables you to specify the child processes and their restart strategies. By effectively utilizing supervisors, you can ensure that your Elixir applications remain resilient, self-healing, and capable of handling unexpected failures without significant downtime.