A Supervisor is a process that monitors other processes in Elixir, managing their lifecycle and ensuring they are restarted if they fail. This promotes fault tolerance in applications.

Supervisors are a fundamental concept in Elixir and are part of the OTP (Open Telecom Platform) design principles, which emphasize building fault-tolerant systems. A Supervisor is a special kind of process whose primary role is to monitor and manage the lifecycle of other processes, known as child processes. The Supervisor uses predefined strategies to determine how to respond when a child process crashes, such as restarting it, stopping the entire supervisor, or ignoring the crash. Common strategies include one-for-one, one-for-all, and rest-for-one, each dictating how child processes should be handled in the event of failure. When implementing a Supervisor, you typically define a module that uses the Supervisor behavior, specifying the child processes it will supervise along with the restart strategy. This allows you to build a hierarchical structure of processes, where Supervisors can oversee other Supervisors, enabling complex systems to be managed effectively. The fault tolerance provided by Supervisors is a key reason why Elixir is well-suited for building reliable and scalable applications. By leveraging Supervisors, developers can create systems that automatically recover from failures, minimizing downtime and ensuring high availability.